<?xml version="1.0" encoding="US-ASCII" standalone="no"?>
<!--Generated by ThunderDome XBRL - 06:00AM UTC 2019-08-02--><link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple"/>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-9-fair-values-of-financial-instruments" xlink:href="mbwm-20190630.xsd#statement-note-9-fair-values-of-financial-instruments" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-9-fair-values-of-financial-instruments" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueDisclosuresTextBlock" xlink:label="us-gaap_FairValueDisclosuresTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_FairValueDisclosuresTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-document-and-entity-information" xlink:href="mbwm-20190630.xsd#statement-document-and-entity-information" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-document-and-entity-information" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_AmendmentFlag" xlink:label="dei_AmendmentFlag" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_CurrentFiscalYearEndDate" xlink:label="dei_CurrentFiscalYearEndDate" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentFiscalPeriodFocus" xlink:label="dei_DocumentFiscalPeriodFocus" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentFiscalYearFocus" xlink:label="dei_DocumentFiscalYearFocus" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentInformationLineItems" xlink:label="dei_DocumentInformationLineItems" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentInformationTable" xlink:label="dei_DocumentInformationTable" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentPeriodEndDate" xlink:label="dei_DocumentPeriodEndDate" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentType" xlink:label="dei_DocumentType" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityCentralIndexKey" xlink:label="dei_EntityCentralIndexKey" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityCommonStockSharesOutstanding" xlink:label="dei_EntityCommonStockSharesOutstanding" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityCurrentReportingStatus" xlink:label="dei_EntityCurrentReportingStatus" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityEmergingGrowthCompany" xlink:label="dei_EntityEmergingGrowthCompany" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityFilerCategory" xlink:label="dei_EntityFilerCategory" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityRegistrantName" xlink:label="dei_EntityRegistrantName" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityShellCompany" xlink:label="dei_EntityShellCompany" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntitySmallBusiness" xlink:label="dei_EntitySmallBusiness" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_Security12bTitle" xlink:label="dei_Security12bTitle" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_TradingSymbol" xlink:label="dei_TradingSymbol" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="dei_DocumentInformationTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentInformationTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityRegistrantName" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityCentralIndexKey" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_TradingSymbol" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_CurrentFiscalYearEndDate" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityFilerCategory" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityCurrentReportingStatus" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityEmergingGrowthCompany" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntitySmallBusiness" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityCommonStockSharesOutstanding" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityShellCompany" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentType" xlink:type="arc"/>
    <link:definitionArc order="12" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentPeriodEndDate" xlink:type="arc"/>
    <link:definitionArc order="13" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentFiscalYearFocus" xlink:type="arc"/>
    <link:definitionArc order="14" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentFiscalPeriodFocus" xlink:type="arc"/>
    <link:definitionArc order="15" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_AmendmentFlag" xlink:type="arc"/>
    <link:definitionArc order="16" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_Security12bTitle" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-condensed-consolidated-balance-sheets-current-period-unaudited-parentheticals" xlink:href="mbwm-20190630.xsd#statement-condensed-consolidated-balance-sheets-current-period-unaudited-parentheticals" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-condensed-consolidated-balance-sheets-current-period-unaudited-parentheticals" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockNoParValue" xlink:label="us-gaap_CommonStockNoParValue" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="us-gaap_CommonStockSharesAuthorized" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="us-gaap_CommonStockSharesIssued" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="us-gaap_CommonStockSharesOutstanding" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PreferredStockNoParValue" xlink:label="us-gaap_PreferredStockNoParValue" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="us-gaap_PreferredStockSharesAuthorized" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="us-gaap_PreferredStockSharesIssued" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PreferredStockNoParValue" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PreferredStockSharesAuthorized" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PreferredStockSharesIssued" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockNoParValue" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockSharesAuthorized" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockSharesOutstanding" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockSharesIssued" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-condensed-consolidated-statements-of-changes-in-shareholders-equity-unaudited-parentheticals" xlink:href="mbwm-20190630.xsd#statement-condensed-consolidated-statements-of-changes-in-shareholders-equity-unaudited-parentheticals" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-condensed-consolidated-statements-of-changes-in-shareholders-equity-unaudited-parentheticals" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockDividendsPerShareCashPaid" xlink:label="us-gaap_CommonStockDividendsPerShareCashPaid" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember" xlink:label="us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="us-gaap_RetainedEarningsMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan" xlink:label="us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:label="us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesIssuedForServices" xlink:label="us-gaap_StockIssuedDuringPeriodSharesIssuedForServices" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodShares" xlink:label="us-gaap_StockRepurchasedAndRetiredDuringPeriodShares" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementEquityComponentsAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_RetainedEarningsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesIssuedForServices" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockDividendsPerShareCashPaid" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockRepurchasedAndRetiredDuringPeriodShares" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-1-significant-accounting-policies" xlink:href="mbwm-20190630.xsd#statement-note-1-significant-accounting-policies" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-1-significant-accounting-policies" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccountingStandardsUpdate201602Member" xlink:label="us-gaap_AccountingStandardsUpdate201602Member" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CoreDepositsMember" xlink:label="us-gaap_CoreDepositsMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="us-gaap_EmployeeStockOptionMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="us-gaap_RestrictedStockMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SignificantAccountingPoliciesTextBlock" xlink:label="us-gaap_SignificantAccountingPoliciesTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="us-gaap_TypeOfAdoptionMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="us-gaap_TypeOfAdoptionMember-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="us-gaap_TypeOfAdoptionMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_AwardTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_RestrictedStockMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_EmployeeStockOptionMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="us-gaap_CoreDepositsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TypeOfAdoptionMember" xlink:to="us-gaap_AccountingStandardsUpdate201602Member" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="us-gaap_TypeOfAdoptionMember-default" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_SignificantAccountingPoliciesTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-2-securities" xlink:href="mbwm-20190630.xsd#statement-note-2-securities" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-2-securities" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AllOtherStatesAndTheirPoliticalSubdivisionsMember" xlink:label="mbwm_AllOtherStatesAndTheirPoliticalSubdivisionsMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_StateOfMichiganAndAllItsPoliticalSubdivisionsMember" xlink:label="mbwm_StateOfMichiganAndAllItsPoliticalSubdivisionsMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_UsGovernmentAgencyDebtObligationsAndMortgageBackedSecuritiesMember" xlink:label="mbwm_UsGovernmentAgencyDebtObligationsAndMortgageBackedSecuritiesMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock" xlink:label="us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_StateOfMichiganAndAllItsPoliticalSubdivisionsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_AllOtherStatesAndTheirPoliticalSubdivisionsMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_UsGovernmentAgencyDebtObligationsAndMortgageBackedSecuritiesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses" xlink:href="mbwm-20190630.xsd#statement-note-3-loans-and-allowance-for-loan-losses" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansNotesTradeAndOtherReceivablesDisclosureTextBlock" xlink:label="us-gaap_LoansNotesTradeAndOtherReceivablesDisclosureTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_LoansNotesTradeAndOtherReceivablesDisclosureTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-4-premises-and-equipment-net" xlink:href="mbwm-20190630.xsd#statement-note-4-premises-and-equipment-net" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-4-premises-and-equipment-net" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" xlink:label="us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-5-deposits" xlink:href="mbwm-20190630.xsd#statement-note-5-deposits" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-5-deposits" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DepositLiabilitiesDisclosuresTextBlock" xlink:label="us-gaap_DepositLiabilitiesDisclosuresTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_DepositLiabilitiesDisclosuresTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-6-securities-sold-under-agreements-to-repurchase" xlink:href="mbwm-20190630.xsd#statement-note-6-securities-sold-under-agreements-to-repurchase" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-6-securities-sold-under-agreements-to-repurchase" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RepurchaseAgreementsResaleAgreementsSecuritiesBorrowedAndSecuritiesLoanedDisclosureTextBlock" xlink:label="us-gaap_RepurchaseAgreementsResaleAgreementsSecuritiesBorrowedAndSecuritiesLoanedDisclosureTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_RepurchaseAgreementsResaleAgreementsSecuritiesBorrowedAndSecuritiesLoanedDisclosureTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-7-federal-home-loan-bank-of-indianapolis-advances" xlink:href="mbwm-20190630.xsd#statement-note-7-federal-home-loan-bank-of-indianapolis-advances" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-7-federal-home-loan-bank-of-indianapolis-advances" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis" xlink:label="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankStateDomain" xlink:label="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankStateDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankStateDomain" xlink:label="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankStateDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_FederalHomeLoanBankOfIndianapolisMember" xlink:label="srt_FederalHomeLoanBankOfIndianapolisMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeMember" xlink:label="srt_RangeMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeMember" xlink:label="srt_RangeMember-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_WeightedAverageMember" xlink:label="srt_WeightedAverageMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FederalHomeLoanBankAdvancesDisclosureTextBlock" xlink:label="us-gaap_FederalHomeLoanBankAdvancesDisclosureTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis" xlink:to="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankStateDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankStateDomain" xlink:to="srt_FederalHomeLoanBankOfIndianapolisMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis" xlink:to="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankStateDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_RangeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_WeightedAverageMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_FederalHomeLoanBankAdvancesDisclosureTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-8-commitments-and-offbalance-sheet-risk" xlink:href="mbwm-20190630.xsd#statement-note-8-commitments-and-offbalance-sheet-risk" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-8-commitments-and-offbalance-sheet-risk" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommitmentsContingenciesAndGuaranteesTextBlock" xlink:label="us-gaap_CommitmentsContingenciesAndGuaranteesTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_CommitmentsContingenciesAndGuaranteesTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-10-fair-values" xlink:href="mbwm-20190630.xsd#statement-note-10-fair-values" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-10-fair-values" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_MunicipalGeneralObligationBondsMember" xlink:label="mbwm_MunicipalGeneralObligationBondsMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateDependentLoansAndForeclosedAssetsEstimatedSellingCostsMember" xlink:label="mbwm_RealEstateDependentLoansAndForeclosedAssetsEstimatedSellingCostsMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateDependentLoansAndForeclosedAssetsMember" xlink:label="mbwm_RealEstateDependentLoansAndForeclosedAssetsMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeMember" xlink:label="srt_RangeMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeMember" xlink:label="srt_RangeMember-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableforsaleSecuritiesMember" xlink:label="us-gaap_AvailableforsaleSecuritiesMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CollateralAxis" xlink:label="us-gaap_CollateralAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CollateralDomain" xlink:label="us-gaap_CollateralDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CollateralDomain" xlink:label="us-gaap_CollateralDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommercialRealEstateMember" xlink:label="us-gaap_CommercialRealEstateMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByAssetClassAxis" xlink:label="us-gaap_FairValueByAssetClassAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementInputsDisclosureTextBlock" xlink:label="us-gaap_FairValueMeasurementInputsDisclosureTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InformationByCategoryOfDebtSecurityAxis" xlink:label="us-gaap_InformationByCategoryOfDebtSecurityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:label="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:label="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ResidentialRealEstateMember" xlink:label="us-gaap_ResidentialRealEstateMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_CollateralAxis" xlink:to="us-gaap_CollateralDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InformationByCategoryOfDebtSecurityAxis" xlink:to="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByAssetClassAxis" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_InformationByCategoryOfDebtSecurityAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:to="us-gaap_AvailableforsaleSecuritiesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_InformationByCategoryOfDebtSecurityAxis" xlink:to="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_MunicipalGeneralObligationBondsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateDependentLoansAndForeclosedAssetsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_CollateralAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CollateralDomain" xlink:to="us-gaap_CommercialRealEstateMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_CollateralAxis" xlink:to="us-gaap_CollateralDomain-default" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_RangeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CollateralDomain" xlink:to="us-gaap_ResidentialRealEstateMember" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FairValueByAssetClassAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:to="mbwm_RealEstateDependentLoansAndForeclosedAssetsEstimatedSellingCostsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByAssetClassAxis" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain-default" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_FairValueMeasurementInputsDisclosureTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-11-regulatory-matters" xlink:href="mbwm-20190630.xsd#statement-note-11-regulatory-matters" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-11-regulatory-matters" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:label="us-gaap_DisclosureTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock" xlink:label="us-gaap_RegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="us-gaap_SubsequentEventMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisclosureTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_SubsequentEventTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventTypeDomain" xlink:to="us-gaap_SubsequentEventMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_RegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-significant-accounting-policies-policies" xlink:href="mbwm-20190630.xsd#statement-significant-accounting-policies-policies" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-significant-accounting-policies-policies" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccountingPoliciesAbstract" xlink:label="us-gaap_AccountingPoliciesAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativesPolicyTextBlock" xlink:label="us-gaap_DerivativesPolicyTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EarningsPerSharePolicyTextBlock" xlink:label="us-gaap_EarningsPerSharePolicyTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinanceLoanAndLeaseReceivablesHeldForInvestmentPolicy" xlink:label="us-gaap_FinanceLoanAndLeaseReceivablesHeldForInvestmentPolicy" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinanceLoanAndLeaseReceivablesHeldForSalePolicy" xlink:label="us-gaap_FinanceLoanAndLeaseReceivablesHeldForSalePolicy" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock" xlink:label="us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansAndLeasesReceivableAllowanceForLoanLossesPolicy" xlink:label="us-gaap_LoansAndLeasesReceivableAllowanceForLoanLossesPolicy" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansAndLeasesReceivableMortgageBankingActivitiesPolicy" xlink:label="us-gaap_LoansAndLeasesReceivableMortgageBankingActivitiesPolicy" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansAndLeasesReceivableTroubledDebtRestructuringPolicy" xlink:label="us-gaap_LoansAndLeasesReceivableTroubledDebtRestructuringPolicy" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MarketableSecuritiesPolicy" xlink:label="us-gaap_MarketableSecuritiesPolicy" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PolicyTextBlockAbstract" xlink:label="us-gaap_PolicyTextBlockAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueFromContractWithCustomerPolicyTextBlock" xlink:label="us-gaap_RevenueFromContractWithCustomerPolicyTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PolicyTextBlockAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PolicyTextBlockAbstract" xlink:to="us-gaap_AccountingPoliciesAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_EarningsPerSharePolicyTextBlock" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_MarketableSecuritiesPolicy" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_FinanceLoanAndLeaseReceivablesHeldForInvestmentPolicy" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_FinanceLoanAndLeaseReceivablesHeldForSalePolicy" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_LoansAndLeasesReceivableMortgageBankingActivitiesPolicy" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_LoansAndLeasesReceivableTroubledDebtRestructuringPolicy" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_LoansAndLeasesReceivableAllowanceForLoanLossesPolicy" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_DerivativesPolicyTextBlock" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_RevenueFromContractWithCustomerPolicyTextBlock" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-2-securities-tables" xlink:href="mbwm-20190630.xsd#statement-note-2-securities-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-2-securities-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueTableTextBlock" xlink:label="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesTextBlock" xlink:label="us-gaap_AvailableForSaleSecuritiesTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InvestmentsClassifiedByContractualMaturityDateTableTextBlock" xlink:label="us-gaap_InvestmentsClassifiedByContractualMaturityDateTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_AvailableForSaleSecuritiesTextBlock" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_InvestmentsClassifiedByContractualMaturityDateTableTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-tables" xlink:href="mbwm-20190630.xsd#statement-note-3-loans-and-allowance-for-loan-losses-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AllowanceRelatedToLoansCategorizedAsTroubledDebtRestructuringsTableTextBlock" xlink:label="mbwm_AllowanceRelatedToLoansCategorizedAsTroubledDebtRestructuringsTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldMovementTableTextBlock" xlink:label="mbwm_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldMovementTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RetailPortfolioSegmentMember" xlink:label="mbwm_RetailPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_TroubleDebtRestructuringActivityTableTextBlock" xlink:label="mbwm_TroubleDebtRestructuringActivityTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_TroubledDebtRestructuringsOnFinancingReceivablesWithInPreviousTwelveMonthsThatBecameOverThirtyDaysPastDueTableTextBlock" xlink:label="mbwm_TroubledDebtRestructuringsOnFinancingReceivablesWithInPreviousTwelveMonthsThatBecameOverThirtyDaysPastDueTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock" xlink:label="us-gaap_AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableCreditQualityIndicatorsTableTextBlock" xlink:label="us-gaap_FinancingReceivableCreditQualityIndicatorsTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ImpairedFinancingReceivablesTableTextBlock" xlink:label="us-gaap_ImpairedFinancingReceivablesTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PastDueFinancingReceivablesTableTextBlock" xlink:label="us-gaap_PastDueFinancingReceivablesTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfFinancingReceivablesNonAccrualStatusTableTextBlock" xlink:label="us-gaap_ScheduleOfFinancingReceivablesNonAccrualStatusTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TroubledDebtRestructuringsOnFinancingReceivablesTableTextBlock" xlink:label="us-gaap_TroubledDebtRestructuringsOnFinancingReceivablesTableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="mbwm_RetailPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="mbwm_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldMovementTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_ScheduleOfFinancingReceivablesNonAccrualStatusTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_PastDueFinancingReceivablesTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_ImpairedFinancingReceivablesTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_FinancingReceivableCreditQualityIndicatorsTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_TroubledDebtRestructuringsOnFinancingReceivablesTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="mbwm_TroubledDebtRestructuringsOnFinancingReceivablesWithInPreviousTwelveMonthsThatBecameOverThirtyDaysPastDueTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="mbwm_TroubleDebtRestructuringActivityTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="mbwm_AllowanceRelatedToLoansCategorizedAsTroubledDebtRestructuringsTableTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-4-premises-and-equipment-net-tables" xlink:href="mbwm-20190630.xsd#statement-note-4-premises-and-equipment-net-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-4-premises-and-equipment-net-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTextBlock" xlink:label="us-gaap_PropertyPlantAndEquipmentTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_PropertyPlantAndEquipmentTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-5-deposits-tables" xlink:href="mbwm-20190630.xsd#statement-note-5-deposits-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-5-deposits-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_SummaryOfDepositsAndPercentageChangeInDepositsTableTextBlock" xlink:label="mbwm_SummaryOfDepositsAndPercentageChangeInDepositsTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="mbwm_SummaryOfDepositsAndPercentageChangeInDepositsTableTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-6-securities-sold-under-agreements-to-repurchase-tables" xlink:href="mbwm-20190630.xsd#statement-note-6-securities-sold-under-agreements-to-repurchase-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-6-securities-sold-under-agreements-to-repurchase-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfRepurchaseAgreements" xlink:label="us-gaap_ScheduleOfRepurchaseAgreements" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_ScheduleOfRepurchaseAgreements" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-7-federal-home-loan-bank-of-indianapolis-advances-tables" xlink:href="mbwm-20190630.xsd#statement-note-7-federal-home-loan-bank-of-indianapolis-advances-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-7-federal-home-loan-bank-of-indianapolis-advances-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_MaturitiesOfCurrentlyOutstandingFhlbAdvancesTableTextBlock" xlink:label="mbwm_MaturitiesOfCurrentlyOutstandingFhlbAdvancesTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="mbwm_MaturitiesOfCurrentlyOutstandingFhlbAdvancesTableTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-8-commitments-and-offbalance-sheet-risk-tables" xlink:href="mbwm-20190630.xsd#statement-note-8-commitments-and-offbalance-sheet-risk-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-8-commitments-and-offbalance-sheet-risk-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_SummaryOfContractualAmountsOfFinancialInstrumentsWithOffBalanceSheetRiskTableTextBlock" xlink:label="mbwm_SummaryOfContractualAmountsOfFinancialInstrumentsWithOffBalanceSheetRiskTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="mbwm_SummaryOfContractualAmountsOfFinancialInstrumentsWithOffBalanceSheetRiskTableTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-9-fair-values-of-financial-instruments-tables" xlink:href="mbwm-20190630.xsd#statement-note-9-fair-values-of-financial-instruments-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-9-fair-values-of-financial-instruments-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByBalanceSheetGroupingTextBlock" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_FairValueByBalanceSheetGroupingTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-10-fair-values-tables" xlink:href="mbwm-20190630.xsd#statement-note-10-fair-values-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-10-fair-values-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnNonrecurringBasisValuationTechniquesTextBlock" xlink:label="us-gaap_FairValueAssetsMeasuredOnNonrecurringBasisValuationTechniquesTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:label="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_FairValueAssetsMeasuredOnNonrecurringBasisValuationTechniquesTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-11-regulatory-matters-tables" xlink:href="mbwm-20190630.xsd#statement-note-11-regulatory-matters-tables" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-11-regulatory-matters-tables" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock" xlink:label="us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TableTextBlock" xlink:label="us-gaap_TableTextBlock" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TableTextBlock" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TableTextBlock" xlink:to="us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-1-significant-accounting-policies-details-textual" xlink:href="mbwm-20190630.xsd#statement-note-1-significant-accounting-policies-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-1-significant-accounting-policies-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_InterestIncomeOnCommercialAndMortgageLoansDiscontinuedPeriod" xlink:label="mbwm_InterestIncomeOnCommercialAndMortgageLoansDiscontinuedPeriod" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_MaximumDelinquencyPeriodForConsumerAndCreditCardLoansToBeChargedOff" xlink:label="mbwm_MaximumDelinquencyPeriodForConsumerAndCreditCardLoansToBeChargedOff" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_NumberOfUnconsolidatedBusinessTrustsFormedToIssueTrustPreferredSecurities" xlink:label="mbwm_NumberOfUnconsolidatedBusinessTrustsFormedToIssueTrustPreferredSecurities" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccountingStandardsUpdate201602Member" xlink:label="us-gaap_AccountingStandardsUpdate201602Member" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife" xlink:label="us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CoreDepositsMember" xlink:label="us-gaap_CoreDepositsMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="us-gaap_EmployeeStockOptionMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToParticipatingNonvestedSharesWithNonForfeitableDividendRights" xlink:label="us-gaap_IncrementalCommonSharesAttributableToParticipatingNonvestedSharesWithNonForfeitableDividendRights" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup" xlink:label="us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeaseLiability" xlink:label="us-gaap_OperatingLeaseLiability" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeaseRightOfUseAsset" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="us-gaap_RestrictedStockMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ServicingAsset" xlink:label="us-gaap_ServicingAsset" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="us-gaap_TypeOfAdoptionMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="us-gaap_TypeOfAdoptionMember-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="us-gaap_TypeOfAdoptionMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_AwardTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_RestrictedStockMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_EmployeeStockOptionMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="us-gaap_CoreDepositsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TypeOfAdoptionMember" xlink:to="us-gaap_AccountingStandardsUpdate201602Member" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="us-gaap_TypeOfAdoptionMember-default" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_NumberOfUnconsolidatedBusinessTrustsFormedToIssueTrustPreferredSecurities" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncrementalCommonSharesAttributableToParticipatingNonvestedSharesWithNonForfeitableDividendRights" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_InterestIncomeOnCommercialAndMortgageLoansDiscontinuedPeriod" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_MaximumDelinquencyPeriodForConsumerAndCreditCardLoansToBeChargedOff" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ServicingAsset" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OperatingLeaseRightOfUseAsset" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OperatingLeaseLiability" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-2-securities-details-textual" xlink:href="mbwm-20190630.xsd#statement-note-2-securities-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-2-securities-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AllOtherStatesAndTheirPoliticalSubdivisionsMember" xlink:label="mbwm_AllOtherStatesAndTheirPoliticalSubdivisionsMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_StateOfMichiganAndAllItsPoliticalSubdivisionsMember" xlink:label="mbwm_StateOfMichiganAndAllItsPoliticalSubdivisionsMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_UsGovernmentAgencyDebtObligationsAndMortgageBackedSecuritiesMember" xlink:label="mbwm_UsGovernmentAgencyDebtObligationsAndMortgageBackedSecuritiesMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleRestricted" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleRestricted" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCreditLossesOnDebtSecuritiesHeld" xlink:label="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCreditLossesOnDebtSecuritiesHeld" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_StateOfMichiganAndAllItsPoliticalSubdivisionsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_AllOtherStatesAndTheirPoliticalSubdivisionsMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_UsGovernmentAgencyDebtObligationsAndMortgageBackedSecuritiesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCreditLossesOnDebtSecuritiesHeld" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleRestricted" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-details-textual" xlink:href="mbwm-20190630.xsd#statement-note-3-loans-and-allowance-for-loan-losses-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_LoansAndLeasesReceivableNonaccrualLoansInterestIncomeRecognized" xlink:label="mbwm_LoansAndLeasesReceivableNonaccrualLoansInterestIncomeRecognized" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_LoansAndLeasesReceivablePercentagePeriodIncreaseDecrease" xlink:label="mbwm_LoansAndLeasesReceivablePercentagePeriodIncreaseDecrease" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_LoansAndLeasesReceivablePeriodIncreaseDecrease" xlink:label="mbwm_LoansAndLeasesReceivablePeriodIncreaseDecrease" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_MinimumNumberOfDaysPastDueAtPeriodEndForLoansModifiedAsTroubledDebtRestructurings" xlink:label="mbwm_MinimumNumberOfDaysPastDueAtPeriodEndForLoansModifiedAsTroubledDebtRestructurings" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet" xlink:label="us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance" xlink:label="us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod" xlink:label="us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans" xlink:label="us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:label="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_LoansAndLeasesReceivablePeriodIncreaseDecrease" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_LoansAndLeasesReceivablePercentagePeriodIncreaseDecrease" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_LoansAndLeasesReceivableNonaccrualLoansInterestIncomeRecognized" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_MinimumNumberOfDaysPastDueAtPeriodEndForLoansModifiedAsTroubledDebtRestructurings" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-4-premises-and-equipment-net-details-textual" xlink:href="mbwm-20190630.xsd#statement-note-4-premises-and-equipment-net-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-4-premises-and-equipment-net-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Depreciation" xlink:label="us-gaap_Depreciation" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_Depreciation" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-5-deposits-details-textual" xlink:href="mbwm-20190630.xsd#statement-note-5-deposits-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-5-deposits-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AggregateIncreaseDecreaseInPercentageOfDeposits" xlink:label="mbwm_AggregateIncreaseDecreaseInPercentageOfDeposits" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Deposits" xlink:label="us-gaap_Deposits" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInDeposits" xlink:label="us-gaap_IncreaseDecreaseInDeposits" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TimeDepositsAtOrAboveFDICInsuranceLimit" xlink:label="us-gaap_TimeDepositsAtOrAboveFDICInsuranceLimit" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_Deposits" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncreaseDecreaseInDeposits" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_AggregateIncreaseDecreaseInPercentageOfDeposits" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TimeDepositsAtOrAboveFDICInsuranceLimit" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-6-securities-sold-under-agreements-to-repurchase-details-textual" xlink:href="mbwm-20190630.xsd#statement-note-6-securities-sold-under-agreements-to-repurchase-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-6-securities-sold-under-agreements-to-repurchase-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyWeightedAverageMaturityOfAgreements1" xlink:label="us-gaap_RepurchaseAgreementCounterpartyWeightedAverageMaturityOfAgreements1" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_RepurchaseAgreementCounterpartyWeightedAverageMaturityOfAgreements1" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-7-federal-home-loan-bank-of-indianapolis-advances-details-textual" xlink:href="mbwm-20190630.xsd#statement-note-7-federal-home-loan-bank-of-indianapolis-advances-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-7-federal-home-loan-bank-of-indianapolis-advances-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis" xlink:label="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankStateDomain" xlink:label="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankStateDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankStateDomain" xlink:label="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankStateDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_FederalHomeLoanBankOfIndianapolisMember" xlink:label="srt_FederalHomeLoanBankOfIndianapolisMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeMember" xlink:label="srt_RangeMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeMember" xlink:label="srt_RangeMember-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_WeightedAverageMember" xlink:label="srt_WeightedAverageMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate" xlink:label="us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd" xlink:label="us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FederalHomeLoanBankAdvancesLongTerm" xlink:label="us-gaap_FederalHomeLoanBankAdvancesLongTerm" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" xlink:label="us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis" xlink:to="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankStateDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankStateDomain" xlink:to="srt_FederalHomeLoanBankOfIndianapolisMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis" xlink:to="srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankStateDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_RangeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_WeightedAverageMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FederalHomeLoanBankAdvancesLongTerm" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-8-commitments-and-offbalance-sheet-risk-details-textual" xlink:href="mbwm-20190630.xsd#statement-note-8-commitments-and-offbalance-sheet-risk-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-8-commitments-and-offbalance-sheet-risk-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_ReserveOrLiabilityBalanceForFinancialInstrumentsWithOffBalanceSheetRisk" xlink:label="mbwm_ReserveOrLiabilityBalanceForFinancialInstrumentsWithOffBalanceSheetRisk" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_ReserveOrLiabilityBalanceForFinancialInstrumentsWithOffBalanceSheetRisk" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-10-fair-values-details-textual" xlink:href="mbwm-20190630.xsd#statement-note-10-fair-values-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-10-fair-values-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_FairValueInputsDiscountFactor" xlink:label="mbwm_FairValueInputsDiscountFactor" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_MunicipalGeneralObligationBondsMember" xlink:label="mbwm_MunicipalGeneralObligationBondsMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateDependentLoansAndForeclosedAssetsEstimatedSellingCostsMember" xlink:label="mbwm_RealEstateDependentLoansAndForeclosedAssetsEstimatedSellingCostsMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateDependentLoansAndForeclosedAssetsMember" xlink:label="mbwm_RealEstateDependentLoansAndForeclosedAssetsMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeMember" xlink:label="srt_RangeMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeMember" xlink:label="srt_RangeMember-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableforsaleSecuritiesMember" xlink:label="us-gaap_AvailableforsaleSecuritiesMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CollateralAxis" xlink:label="us-gaap_CollateralAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CollateralDomain" xlink:label="us-gaap_CollateralDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CollateralDomain" xlink:label="us-gaap_CollateralDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommercialRealEstateMember" xlink:label="us-gaap_CommercialRealEstateMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByAssetClassAxis" xlink:label="us-gaap_FairValueByAssetClassAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InformationByCategoryOfDebtSecurityAxis" xlink:label="us-gaap_InformationByCategoryOfDebtSecurityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup" xlink:label="us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:label="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:label="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ResidentialRealEstateMember" xlink:label="us-gaap_ResidentialRealEstateMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ValuationAllowancesAndReservesBalance" xlink:label="us-gaap_ValuationAllowancesAndReservesBalance" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_CollateralAxis" xlink:to="us-gaap_CollateralDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InformationByCategoryOfDebtSecurityAxis" xlink:to="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByAssetClassAxis" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_InformationByCategoryOfDebtSecurityAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:to="us-gaap_AvailableforsaleSecuritiesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_InformationByCategoryOfDebtSecurityAxis" xlink:to="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_MunicipalGeneralObligationBondsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateDependentLoansAndForeclosedAssetsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_CollateralAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CollateralDomain" xlink:to="us-gaap_CommercialRealEstateMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_CollateralAxis" xlink:to="us-gaap_CollateralDomain-default" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_RangeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CollateralDomain" xlink:to="us-gaap_ResidentialRealEstateMember" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FairValueByAssetClassAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:to="mbwm_RealEstateDependentLoansAndForeclosedAssetsEstimatedSellingCostsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByAssetClassAxis" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain-default" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ValuationAllowancesAndReservesBalance" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_FairValueInputsDiscountFactor" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-11-regulatory-matters-details-textual" xlink:href="mbwm-20190630.xsd#statement-note-11-regulatory-matters-details-textual" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-11-regulatory-matters-details-textual" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_CapitalConservationBuffer" xlink:label="mbwm_CapitalConservationBuffer" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_MaximumLevelOfConsolidatedAggregateAssetsAllowingForInclusionOfTrustPreferredSecuritiesInTierOneCapital" xlink:label="mbwm_MaximumLevelOfConsolidatedAggregateAssetsAllowingForInclusionOfTrustPreferredSecuritiesInTierOneCapital" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_MaximumRestrictedCoreElementAllowedInTierOneCapitalPercent" xlink:label="mbwm_MaximumRestrictedCoreElementAllowedInTierOneCapitalPercent" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_PreferredSecuritiesOfSubsidiaryTrust" xlink:label="mbwm_PreferredSecuritiesOfSubsidiaryTrust" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_StockRepurchaseProgramAdditionalAuthorizedAmount" xlink:label="mbwm_StockRepurchaseProgramAdditionalAuthorizedAmount" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockDividendsPerShareDeclared" xlink:label="us-gaap_CommonStockDividendsPerShareDeclared" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DividendPayableDateToBePaidDayMonthAndYear" xlink:label="us-gaap_DividendPayableDateToBePaidDayMonthAndYear" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockRepurchaseProgramAuthorizedAmount1" xlink:label="us-gaap_StockRepurchaseProgramAuthorizedAmount1" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockRepurchasedDuringPeriodShares" xlink:label="us-gaap_StockRepurchasedDuringPeriodShares" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockRepurchasedDuringPeriodValue" xlink:label="us-gaap_StockRepurchasedDuringPeriodValue" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="us-gaap_SubsequentEventMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TreasuryStockAcquiredAverageCostPerShare" xlink:label="us-gaap_TreasuryStockAcquiredAverageCostPerShare" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_SubsequentEventTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SubsequentEventTypeDomain" xlink:to="us-gaap_SubsequentEventMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_PreferredSecuritiesOfSubsidiaryTrust" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_MaximumRestrictedCoreElementAllowedInTierOneCapitalPercent" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_MaximumLevelOfConsolidatedAggregateAssetsAllowingForInclusionOfTrustPreferredSecuritiesInTierOneCapital" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_CapitalConservationBuffer" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockDividendsPerShareDeclared" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DividendPayableDateToBePaidDayMonthAndYear" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockRepurchaseProgramAuthorizedAmount1" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_StockRepurchaseProgramAdditionalAuthorizedAmount" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockRepurchasedDuringPeriodShares" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockRepurchasedDuringPeriodValue" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TreasuryStockAcquiredAverageCostPerShare" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-acquired-impaired-loans-accretable-yield-details" xlink:href="mbwm-20190630.xsd#statement-note-3-loans-and-allowance-for-loan-losses-acquired-impaired-loans-accretable-yield-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-acquired-impaired-loans-accretable-yield-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield" xlink:label="us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion" xlink:label="us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAdditions" xlink:label="us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAdditions" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldDisposalsOfLoans" xlink:label="us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldDisposalsOfLoans" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldReclassificationsFromNonaccretableDifference" xlink:label="us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldReclassificationsFromNonaccretableDifference" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAdditions" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldReclassificationsFromNonaccretableDifference" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldDisposalsOfLoans" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-7-federal-home-loan-bank-of-indianapolis-advances-maturities-of-currently-outstanding-fhlb-advances-details" xlink:href="mbwm-20190630.xsd#statement-note-7-federal-home-loan-bank-of-indianapolis-advances-maturities-of-currently-outstanding-fhlb-advances-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-7-federal-home-loan-bank-of-indianapolis-advances-maturities-of-currently-outstanding-fhlb-advances-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueAfterFiveYearsOfBalanceSheetDate" xlink:label="us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueAfterFiveYearsOfBalanceSheetDate" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromFourToFiveYearsOfBalanceSheetDate" xlink:label="us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromFourToFiveYearsOfBalanceSheetDate" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromOneToTwoYearsOfBalanceSheetDate" xlink:label="us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromOneToTwoYearsOfBalanceSheetDate" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromThreeToFourYearsOfBalanceSheetDate" xlink:label="us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromThreeToFourYearsOfBalanceSheetDate" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromTwoToThreeYearsOfBalanceSheetDate" xlink:label="us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromTwoToThreeYearsOfBalanceSheetDate" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueInRemainderOfFiscalYear" xlink:label="us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueInRemainderOfFiscalYear" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueInRemainderOfFiscalYear" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromOneToTwoYearsOfBalanceSheetDate" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromTwoToThreeYearsOfBalanceSheetDate" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromThreeToFourYearsOfBalanceSheetDate" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromFourToFiveYearsOfBalanceSheetDate" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueAfterFiveYearsOfBalanceSheetDate" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-condensed-consolidated-balance-sheets-current-period-unaudited" xlink:href="mbwm-20190630.xsd#statement-condensed-consolidated-balance-sheets-current-period-unaudited" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-condensed-consolidated-balance-sheets-current-period-unaudited" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccruedLiabilitiesCurrentAndNoncurrent" xlink:label="us-gaap_AccruedLiabilitiesCurrentAndNoncurrent" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Assets" xlink:label="us-gaap_Assets" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="us-gaap_AssetsAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_BankOwnedLifeInsurance" xlink:label="us-gaap_BankOwnedLifeInsurance" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashAndDueFromBanks" xlink:label="us-gaap_CashAndDueFromBanks" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashCashEquivalentsAndFederalFundsSold" xlink:label="us-gaap_CashCashEquivalentsAndFederalFundsSold" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="us-gaap_CommitmentsAndContingencies" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockValue" xlink:label="us-gaap_CommonStockValue" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Deposits" xlink:label="us-gaap_Deposits" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FederalHomeLoanBankAdvancesLongTerm" xlink:label="us-gaap_FederalHomeLoanBankAdvancesLongTerm" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FederalHomeLoanBankStock" xlink:label="us-gaap_FederalHomeLoanBankStock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Goodwill" xlink:label="us-gaap_Goodwill" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestBearingDepositLiabilitiesDomestic" xlink:label="us-gaap_InterestBearingDepositLiabilitiesDomestic" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestBearingDepositsInBanks" xlink:label="us-gaap_InterestBearingDepositsInBanks" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust" xlink:label="us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Liabilities" xlink:label="us-gaap_Liabilities" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansAndLeasesReceivableAllowance" xlink:label="us-gaap_LoansAndLeasesReceivableAllowance" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:label="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetReportedAmount" xlink:label="us-gaap_LoansAndLeasesReceivableNetReportedAmount" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NoninterestBearingDomesticDepositDemand" xlink:label="us-gaap_NoninterestBearingDomesticDepositDemand" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherAssets" xlink:label="us-gaap_OtherAssets" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PreferredStockValue" xlink:label="us-gaap_PreferredStockValue" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="us-gaap_PropertyPlantAndEquipmentNet" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SecuritiesSoldUnderAgreementsToRepurchase" xlink:label="us-gaap_SecuritiesSoldUnderAgreementsToRepurchase" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="us-gaap_StockholdersEquityAbstract" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AssetsAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_CashAndDueFromBanks" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_InterestBearingDepositsInBanks" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_CashCashEquivalentsAndFederalFundsSold" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_FederalHomeLoanBankStock" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_LoansAndLeasesReceivableAllowance" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_LoansAndLeasesReceivableNetReportedAmount" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_PropertyPlantAndEquipmentNet" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_BankOwnedLifeInsurance" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_Goodwill" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsNet" xlink:type="arc"/>
    <link:definitionArc order="12" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_OtherAssets" xlink:type="arc"/>
    <link:definitionArc order="13" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_Assets" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_NoninterestBearingDomesticDepositDemand" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_InterestBearingDepositLiabilitiesDomestic" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_Deposits" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_SecuritiesSoldUnderAgreementsToRepurchase" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_FederalHomeLoanBankAdvancesLongTerm" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_AccruedLiabilitiesCurrentAndNoncurrent" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_Liabilities" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_CommitmentsAndContingencies" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockholdersEquityAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_PreferredStockValue" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_CommonStockValue" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_StockholdersEquity" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-condensed-consolidated-statements-of-income-unaudited" xlink:href="mbwm-20190630.xsd#statement-condensed-consolidated-statements-of-income-unaudited" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-condensed-consolidated-statements-of-income-unaudited" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_FeesAndCommissionsPayrollProcessing" xlink:label="mbwm_FeesAndCommissionsPayrollProcessing" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductOrServiceAxis" xlink:label="srt_ProductOrServiceAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_BankOwnedLifeInsuranceIncome" xlink:label="us-gaap_BankOwnedLifeInsuranceIncome" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockDividendsPerShareCashPaid" xlink:label="us-gaap_CommonStockDividendsPerShareCashPaid" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CreditAndDebitCardMember" xlink:label="us-gaap_CreditAndDebitCardMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DepositAccountMember" xlink:label="us-gaap_DepositAccountMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EarningsPerShareBasic" xlink:label="us-gaap_EarningsPerShareBasic" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="us-gaap_EarningsPerShareDiluted" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquipmentExpense" xlink:label="us-gaap_EquipmentExpense" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="us-gaap_IncomeTaxExpenseBenefit" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InformationTechnologyAndDataProcessing" xlink:label="us-gaap_InformationTechnologyAndDataProcessing" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestAndDividendIncomeOperating" xlink:label="us-gaap_InterestAndDividendIncomeOperating" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:label="us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestAndFeeIncomeLoansAndLeases" xlink:label="us-gaap_InterestAndFeeIncomeLoansAndLeases" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestExpense" xlink:label="us-gaap_InterestExpense" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestExpenseAbstract" xlink:label="us-gaap_InterestExpenseAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestExpenseDeposits" xlink:label="us-gaap_InterestExpenseDeposits" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestExpenseFederalHomeLoanBankAndFederalReserveBankAdvancesLongTerm" xlink:label="us-gaap_InterestExpenseFederalHomeLoanBankAndFederalReserveBankAdvancesLongTerm" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestExpenseShortTermBorrowings" xlink:label="us-gaap_InterestExpenseShortTermBorrowings" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestExpenseSubordinatedNotesAndDebentures" xlink:label="us-gaap_InterestExpenseSubordinatedNotesAndDebentures" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestIncomeDepositsWithFinancialInstitutions" xlink:label="us-gaap_InterestIncomeDepositsWithFinancialInstitutions" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss" xlink:label="us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestIncomeExpenseNet" xlink:label="us-gaap_InterestIncomeExpenseNet" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestIncomeSecuritiesTaxExempt" xlink:label="us-gaap_InterestIncomeSecuritiesTaxExempt" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestIncomeSecuritiesTaxable" xlink:label="us-gaap_InterestIncomeSecuritiesTaxable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LaborAndRelatedExpense" xlink:label="us-gaap_LaborAndRelatedExpense" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MortgageBankingMember" xlink:label="us-gaap_MortgageBankingMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NoninterestExpense" xlink:label="us-gaap_NoninterestExpense" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NoninterestExpenseAbstract" xlink:label="us-gaap_NoninterestExpenseAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NoninterestIncome" xlink:label="us-gaap_NoninterestIncome" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NoninterestIncomeAbstract" xlink:label="us-gaap_NoninterestIncomeAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NoninterestIncomeOtherOperatingIncome" xlink:label="us-gaap_NoninterestIncomeOtherOperatingIncome" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OccupancyNet" xlink:label="us-gaap_OccupancyNet" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherNoninterestExpense" xlink:label="us-gaap_OtherNoninterestExpense" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProvisionForLoanAndLeaseLosses" xlink:label="us-gaap_ProvisionForLoanAndLeaseLosses" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax" xlink:label="us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_ProductOrServiceAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="us-gaap_DepositAccountMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="us-gaap_CreditAndDebitCardMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="us-gaap_MortgageBankingMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:to="us-gaap_InterestAndFeeIncomeLoansAndLeases" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:to="us-gaap_InterestIncomeSecuritiesTaxable" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:to="us-gaap_InterestIncomeSecuritiesTaxExempt" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:to="us-gaap_InterestIncomeDepositsWithFinancialInstitutions" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:to="us-gaap_InterestAndDividendIncomeOperating" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InterestExpenseAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestExpenseAbstract" xlink:to="us-gaap_InterestExpenseDeposits" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestExpenseAbstract" xlink:to="us-gaap_InterestExpenseShortTermBorrowings" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestExpenseAbstract" xlink:to="us-gaap_InterestExpenseFederalHomeLoanBankAndFederalReserveBankAdvancesLongTerm" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestExpenseAbstract" xlink:to="us-gaap_InterestExpenseSubordinatedNotesAndDebentures" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestExpenseAbstract" xlink:to="us-gaap_InterestExpense" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestExpenseAbstract" xlink:to="us-gaap_InterestIncomeExpenseNet" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestExpenseAbstract" xlink:to="us-gaap_ProvisionForLoanAndLeaseLosses" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestExpenseAbstract" xlink:to="us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NoninterestIncomeAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestIncomeAbstract" xlink:to="us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestIncomeAbstract" xlink:to="us-gaap_BankOwnedLifeInsuranceIncome" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestIncomeAbstract" xlink:to="mbwm_FeesAndCommissionsPayrollProcessing" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestIncomeAbstract" xlink:to="us-gaap_NoninterestIncomeOtherOperatingIncome" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestIncomeAbstract" xlink:to="us-gaap_NoninterestIncome" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NoninterestExpenseAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_LaborAndRelatedExpense" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_OccupancyNet" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_EquipmentExpense" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_InformationTechnologyAndDataProcessing" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_OtherNoninterestExpense" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_NoninterestExpense" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_IncomeTaxExpenseBenefit" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_NetIncomeLoss" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_EarningsPerShareBasic" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_EarningsPerShareDiluted" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_CommonStockDividendsPerShareCashPaid" xlink:type="arc"/>
    <link:definitionArc order="12" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:type="arc"/>
    <link:definitionArc order="13" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-condensed-consolidated-statements-of-cash-flows-unaudited" xlink:href="mbwm-20190630.xsd#statement-condensed-consolidated-statements-of-cash-flows-unaudited" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-condensed-consolidated-statements-of-cash-flows-unaudited" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_DiscountAccretionOnAcquiredLoans" xlink:label="mbwm_DiscountAccretionOnAcquiredLoans" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_NetGainLossFromSaleAndValuationWriteDownOfForeclosedAssets" xlink:label="mbwm_NetGainLossFromSaleAndValuationWriteDownOfForeclosedAssets" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_NetGainLossFromSaleAndValuationWriteDownOfFormerBankPremises" xlink:label="mbwm_NetGainLossFromSaleAndValuationWriteDownOfFormerBankPremises" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_ProceedsFromSaleOfFormerBankPremises" xlink:label="mbwm_ProceedsFromSaleOfFormerBankPremises" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_TransferOfBankPremisesToOtherRealEstateOwned" xlink:label="mbwm_TransferOfBankPremisesToOtherRealEstateOwned" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_BankOwnedLifeInsuranceIncome" xlink:label="us-gaap_BankOwnedLifeInsuranceIncome" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashCashEquivalentsAndFederalFundsSold" xlink:label="us-gaap_CashCashEquivalentsAndFederalFundsSold" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DepreciationAmortizationAndAccretionNet" xlink:label="us-gaap_DepreciationAmortizationAndAccretionNet" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_GainLossOnSaleOfMortgageLoans" xlink:label="us-gaap_GainLossOnSaleOfMortgageLoans" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_GainLossOnSaleOfPropertyPlantEquipment" xlink:label="us-gaap_GainLossOnSaleOfPropertyPlantEquipment" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeTaxesPaidNet" xlink:label="us-gaap_IncomeTaxesPaidNet" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet" xlink:label="us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities" xlink:label="us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInOtherDeposits" xlink:label="us-gaap_IncreaseDecreaseInOtherDeposits" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInTimeDeposits" xlink:label="us-gaap_IncreaseDecreaseInTimeDeposits" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestPaidNet" xlink:label="us-gaap_InterestPaidNet" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" xlink:label="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsForOriginationOfMortgageLoansHeldForSale" xlink:label="us-gaap_PaymentsForOriginationOfMortgageLoansHeldForSale" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsForProceedsFromLoansAndLeases" xlink:label="us-gaap_PaymentsForProceedsFromLoansAndLeases" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsForProceedsFromProductiveAssets" xlink:label="us-gaap_PaymentsForProceedsFromProductiveAssets" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:label="us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsOfDividendsCommonStock" xlink:label="us-gaap_PaymentsOfDividendsCommonStock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsToAcquireAvailableForSaleSecurities" xlink:label="us-gaap_PaymentsToAcquireAvailableForSaleSecurities" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsToAcquireFederalHomeLoanBankStock" xlink:label="us-gaap_PaymentsToAcquireFederalHomeLoanBankStock" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsToAcquireLifeInsurancePolicies" xlink:label="us-gaap_PaymentsToAcquireLifeInsurancePolicies" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromFederalHomeLoanBankAdvances" xlink:label="us-gaap_ProceedsFromFederalHomeLoanBankAdvances" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStockDividendReinvestmentPlan" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStockDividendReinvestmentPlan" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromLifeInsurancePolicies" xlink:label="us-gaap_ProceedsFromLifeInsurancePolicies" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" xlink:label="us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromPaymentsForInSecuritiesSoldUnderAgreementsToRepurchase" xlink:label="us-gaap_ProceedsFromPaymentsForInSecuritiesSoldUnderAgreementsToRepurchase" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromSaleOfForeclosedAssets" xlink:label="us-gaap_ProceedsFromSaleOfForeclosedAssets" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromSaleOfMortgageLoansHeldForSale" xlink:label="us-gaap_ProceedsFromSaleOfMortgageLoansHeldForSale" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromStockOptionsExercised" xlink:label="us-gaap_ProceedsFromStockOptionsExercised" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromStockPlans" xlink:label="us-gaap_ProceedsFromStockPlans" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProvisionForLoanAndLeaseLosses" xlink:label="us-gaap_ProvisionForLoanAndLeaseLosses" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RepaymentsOfFederalHomeLoanBankBorrowings" xlink:label="us-gaap_RepaymentsOfFederalHomeLoanBankBorrowings" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="us-gaap_ShareBasedCompensation" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransferToOtherRealEstate" xlink:label="us-gaap_TransferToOtherRealEstate" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_NetIncomeLoss" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_DepreciationAmortizationAndAccretionNet" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="mbwm_DiscountAccretionOnAcquiredLoans" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_ProvisionForLoanAndLeaseLosses" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_ShareBasedCompensation" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromSaleOfMortgageLoansHeldForSale" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_PaymentsForOriginationOfMortgageLoansHeldForSale" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_GainLossOnSaleOfMortgageLoans" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="mbwm_NetGainLossFromSaleAndValuationWriteDownOfForeclosedAssets" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="mbwm_NetGainLossFromSaleAndValuationWriteDownOfFormerBankPremises" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_GainLossOnSaleOfPropertyPlantEquipment" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_BankOwnedLifeInsuranceIncome" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsForProceedsFromLoansAndLeases" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquireAvailableForSaleSecurities" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromSaleOfForeclosedAssets" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="mbwm_ProceedsFromSaleOfFormerBankPremises" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquireFederalHomeLoanBankStock" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquireLifeInsurancePolicies" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromLifeInsurancePolicies" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsForProceedsFromProductiveAssets" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_IncreaseDecreaseInTimeDeposits" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_IncreaseDecreaseInOtherDeposits" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromPaymentsForInSecuritiesSoldUnderAgreementsToRepurchase" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_RepaymentsOfFederalHomeLoanBankBorrowings" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromFederalHomeLoanBankAdvances" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromStockOptionsExercised" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromStockPlans" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromIssuanceOfCommonStockDividendReinvestmentPlan" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_PaymentsOfDividendsCommonStock" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:type="arc"/>
    <link:definitionArc order="12" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_CashCashEquivalentsAndFederalFundsSold" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SupplementalCashFlowInformationAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="us-gaap_InterestPaidNet" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="us-gaap_IncomeTaxesPaidNet" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="us-gaap_TransferToOtherRealEstate" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="mbwm_TransferOfBankPremisesToOtherRealEstateOwned" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-condensed-consolidated-statements-of-comprehensive-income-unaudited" xlink:href="mbwm-20190630.xsd#statement-condensed-consolidated-statements-of-comprehensive-income-unaudited" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-condensed-consolidated-statements-of-comprehensive-income-unaudited" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTax" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxAttributableToParentAbstract" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTaxAttributableToParentAbstract" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1" xlink:label="us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodBeforeTax" xlink:label="us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodBeforeTax" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax" xlink:label="us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax" xlink:label="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax" xlink:label="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetIncomeLoss" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherComprehensiveIncomeLossNetOfTaxAttributableToParentAbstract" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OtherComprehensiveIncomeLossNetOfTaxAttributableToParentAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OtherComprehensiveIncomeLossNetOfTaxAttributableToParentAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodBeforeTax" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OtherComprehensiveIncomeLossNetOfTaxAttributableToParentAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OtherComprehensiveIncomeLossNetOfTaxAttributableToParentAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OtherComprehensiveIncomeLossNetOfTaxAttributableToParentAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OtherComprehensiveIncomeLossNetOfTaxAttributableToParentAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OtherComprehensiveIncomeLossNetOfTaxAttributableToParentAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OtherComprehensiveIncomeLossNetOfTaxAttributableToParentAbstract" xlink:to="us-gaap_ComprehensiveIncomeNetOfTax" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-condensed-consolidated-statements-of-changes-in-shareholders-equity-unaudited" xlink:href="mbwm-20190630.xsd#statement-condensed-consolidated-statements-of-changes-in-shareholders-equity-unaudited" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-condensed-consolidated-statements-of-changes-in-shareholders-equity-unaudited" xlink:type="extended">
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_ReclassificationOfEquitySecuritiesRelatedToAsu201601Adoption" xlink:label="mbwm_ReclassificationOfEquitySecuritiesRelatedToAsu201601Adoption" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember" xlink:label="us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DividendsCommonStockCash" xlink:label="us-gaap_DividendsCommonStockCash" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax" xlink:label="us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:label="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PreferredStockMember" xlink:label="us-gaap_PreferredStockMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="us-gaap_RetainedEarningsMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan" xlink:label="us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:label="us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueIssuedForServices" xlink:label="us-gaap_StockIssuedDuringPeriodValueIssuedForServices" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:label="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue" xlink:label="us-gaap_StockRepurchasedAndRetiredDuringPeriodValue" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementEquityComponentsAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_PreferredStockMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_RetainedEarningsMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockholdersEquity" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueIssuedForServices" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DividendsCommonStockCash" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetIncomeLoss" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockRepurchasedAndRetiredDuringPeriodValue" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_ReclassificationOfEquitySecuritiesRelatedToAsu201601Adoption" xlink:type="arc"/>
    <link:definitionArc order="12" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-2-securities-availableforsale-securities-details" xlink:href="mbwm-20190630.xsd#statement-note-2-securities-availableforsale-securities-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-2-securities-availableforsale-securities-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_MunicipalGeneralObligationBondsMember" xlink:label="mbwm_MunicipalGeneralObligationBondsMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_MunicipalRevenueBondsMember" xlink:label="mbwm_MunicipalRevenueBondsMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OtherDebtAndEquitySecuritiesMember" xlink:label="mbwm_OtherDebtAndEquitySecuritiesMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MortgageBackedSecuritiesMember" xlink:label="us-gaap_MortgageBackedSecuritiesMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:label="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_MortgageBackedSecuritiesMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_MunicipalGeneralObligationBondsMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_MunicipalRevenueBondsMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_OtherDebtAndEquitySecuritiesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-2-securities-debt-securities-by-maturity-details" xlink:href="mbwm-20190630.xsd#statement-note-2-securities-debt-securities-by-maturity-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-2-securities-debt-securities-by-maturity-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OtherDebtAndEquitySecuritiesMember" xlink:label="mbwm_OtherDebtAndEquitySecuritiesMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_WeightedAverageYieldOfSecuritiesPortfolio" xlink:label="mbwm_WeightedAverageYieldOfSecuritiesPortfolio" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueAftertenYears" xlink:label="mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueAftertenYears" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueFromFiveToTenYears" xlink:label="mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueFromFiveToTenYears" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueFromOneToFiveYears" xlink:label="mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueFromOneToFiveYears" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueInOneYearOrLess" xlink:label="mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueInOneYearOrLess" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_WeightedAverageYieldOfSecuritiesPortfolioNoSingleMaturity" xlink:label="mbwm_WeightedAverageYieldOfSecuritiesPortfolioNoSingleMaturity" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRemainderOfFiscalYearAmortizedCostBasis" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRemainderOfFiscalYearAmortizedCostBasis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRemainderOfFiscalYearFairValue" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRemainderOfFiscalYearFairValue" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MortgageBackedSecuritiesMember" xlink:label="us-gaap_MortgageBackedSecuritiesMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_MortgageBackedSecuritiesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_OtherDebtAndEquitySecuritiesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueInOneYearOrLess" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRemainderOfFiscalYearAmortizedCostBasis" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRemainderOfFiscalYearFairValue" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueFromOneToFiveYears" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueFromFiveToTenYears" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_WeightedAverageYieldOfSecuritiesPortfolioDueAftertenYears" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost" xlink:type="arc"/>
    <link:definitionArc order="12" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue" xlink:type="arc"/>
    <link:definitionArc order="13" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_WeightedAverageYieldOfSecuritiesPortfolioNoSingleMaturity" xlink:type="arc"/>
    <link:definitionArc order="14" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost" xlink:type="arc"/>
    <link:definitionArc order="15" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" xlink:type="arc"/>
    <link:definitionArc order="16" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_WeightedAverageYieldOfSecuritiesPortfolio" xlink:type="arc"/>
    <link:definitionArc order="17" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:type="arc"/>
    <link:definitionArc order="18" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-nonperforming-loans-details" xlink:href="mbwm-20190630.xsd#statement-note-3-loans-and-allowance-for-loan-losses-nonperforming-loans-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-nonperforming-loans-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AcquiredLoanMember" xlink:label="mbwm_AcquiredLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_CommercialAndIndustrialMember" xlink:label="mbwm_CommercialAndIndustrialMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans" xlink:label="mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_HomeEquityAndOtherMember" xlink:label="mbwm_HomeEquityAndOtherMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OneToFourFamilyMortgagesMember" xlink:label="mbwm_OneToFourFamilyMortgagesMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OriginatedLoanMember" xlink:label="mbwm_OriginatedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:label="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RetailPortfolioSegmentMember" xlink:label="mbwm_RetailPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:label="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentPerformanceStatusAxis" xlink:label="us-gaap_FinancialInstrumentPerformanceStatusAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentPerformanceStatusDomain" xlink:label="us-gaap_FinancialInstrumentPerformanceStatusDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentPerformanceStatusDomain" xlink:label="us-gaap_FinancialInstrumentPerformanceStatusDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" xlink:label="us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NonperformingFinancingReceivableMember" xlink:label="us-gaap_NonperformingFinancingReceivableMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentPerformanceStatusAxis" xlink:to="us-gaap_FinancialInstrumentPerformanceStatusDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentPerformanceStatusAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancialInstrumentPerformanceStatusDomain" xlink:to="us-gaap_NonperformingFinancingReceivableMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentPerformanceStatusAxis" xlink:to="us-gaap_FinancialInstrumentPerformanceStatusDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_OriginatedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_AcquiredLoanMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_CommercialAndIndustrialMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="mbwm_RetailPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_HomeEquityAndOtherMember" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_OneToFourFamilyMortgagesMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_FinancingReceivablePastDueNinetyDaysOrMoreAndStillAccruingInterestAndNonaccrualLoans" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-retail-credit-exposure-details" xlink:href="mbwm-20190630.xsd#statement-note-3-loans-and-allowance-for-loan-losses-retail-credit-exposure-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-retail-credit-exposure-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AcquiredLoanMember" xlink:label="mbwm_AcquiredLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_HomeEquityAndOtherMember" xlink:label="mbwm_HomeEquityAndOtherMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OneToFourFamilyMortgagesMember" xlink:label="mbwm_OneToFourFamilyMortgagesMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OriginatedLoanMember" xlink:label="mbwm_OriginatedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RetailPortfolioSegmentMember" xlink:label="mbwm_RetailPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:label="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_OriginatedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="mbwm_RetailPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_HomeEquityAndOtherMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_AcquiredLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_OneToFourFamilyMortgagesMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-loans-modified-as-troubled-debt-restructurings-within-the-previous-twelve-months-that-became-over-30-days-past-due-details" xlink:href="mbwm-20190630.xsd#statement-note-3-loans-and-allowance-for-loan-losses-loans-modified-as-troubled-debt-restructurings-within-the-previous-twelve-months-that-became-over-30-days-past-due-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-loans-modified-as-troubled-debt-restructurings-within-the-previous-twelve-months-that-became-over-30-days-past-due-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AcquiredLoanMember" xlink:label="mbwm_AcquiredLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_CommercialAndIndustrialMember" xlink:label="mbwm_CommercialAndIndustrialMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_HomeEquityAndOtherMember" xlink:label="mbwm_HomeEquityAndOtherMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OneToFourFamilyMortgagesMember" xlink:label="mbwm_OneToFourFamilyMortgagesMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OriginatedLoanMember" xlink:label="mbwm_OriginatedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:label="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RetailPortfolioSegmentMember" xlink:label="mbwm_RetailPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:label="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1" xlink:label="us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1" xlink:label="us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_OriginatedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_CommercialAndIndustrialMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_AcquiredLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="mbwm_RetailPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_HomeEquityAndOtherMember" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_OneToFourFamilyMortgagesMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-4-premises-and-equipment-net-summary-of-premises-and-equipment-details" xlink:href="mbwm-20190630.xsd#statement-note-4-premises-and-equipment-net-summary-of-premises-and-equipment-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-4-premises-and-equipment-net-summary-of-premises-and-equipment-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_BuildingMember" xlink:label="us-gaap_BuildingMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="us-gaap_FurnitureAndFixturesMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LandAndLandImprovementsMember" xlink:label="us-gaap_LandAndLandImprovementsMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="us-gaap_PropertyPlantAndEquipmentGross" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="us-gaap_PropertyPlantAndEquipmentNet" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_LandAndLandImprovementsMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_BuildingMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_FurnitureAndFixturesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PropertyPlantAndEquipmentGross" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PropertyPlantAndEquipmentNet" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-6-securities-sold-under-agreements-to-repurchase-securities-sold-under-agreement-to-repurchase-details" xlink:href="mbwm-20190630.xsd#statement-note-6-securities-sold-under-agreements-to-repurchase-securities-sold-under-agreement-to-repurchase-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-6-securities-sold-under-agreements-to-repurchase-securities-sold-under-agreement-to-repurchase-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentInterestRateDuringPeriod" xlink:label="us-gaap_DebtInstrumentInterestRateDuringPeriod" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SecuritiesSoldUnderAgreementsToRepurchase" xlink:label="us-gaap_SecuritiesSoldUnderAgreementsToRepurchase" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseMember" xlink:label="us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShortTermDebtTypeAxis" xlink:label="us-gaap_ShortTermDebtTypeAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShortTermDebtTypeDomain" xlink:label="us-gaap_ShortTermDebtTypeDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShortTermDebtTypeDomain" xlink:label="us-gaap_ShortTermDebtTypeDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShortTermDebtWeightedAverageInterestRate" xlink:label="us-gaap_ShortTermDebtWeightedAverageInterestRate" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShorttermDebtAverageOutstandingAmount" xlink:label="us-gaap_ShorttermDebtAverageOutstandingAmount" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShorttermDebtMaximumAmountOutstandingDuringPeriod" xlink:label="us-gaap_ShorttermDebtMaximumAmountOutstandingDuringPeriod" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_ShortTermDebtTypeAxis" xlink:to="us-gaap_ShortTermDebtTypeDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_ShortTermDebtTypeAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShortTermDebtTypeDomain" xlink:to="us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_ShortTermDebtTypeAxis" xlink:to="us-gaap_ShortTermDebtTypeDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SecuritiesSoldUnderAgreementsToRepurchase" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ShortTermDebtWeightedAverageInterestRate" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ShorttermDebtAverageOutstandingAmount" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DebtInstrumentInterestRateDuringPeriod" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ShorttermDebtMaximumAmountOutstandingDuringPeriod" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-8-commitments-and-offbalance-sheet-risk-exposure-to-credit-losses-details" xlink:href="mbwm-20190630.xsd#statement-note-8-commitments-and-offbalance-sheet-risk-exposure-to-credit-losses-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-8-commitments-and-offbalance-sheet-risk-exposure-to-credit-losses-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_ConsumerOtherFinancingReceivable1Member" xlink:label="mbwm_ConsumerOtherFinancingReceivable1Member" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OneToFourFamilyMortgagesMember" xlink:label="mbwm_OneToFourFamilyMortgagesMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:label="us-gaap_ConsumerPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="us-gaap_CreditFacilityAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="us-gaap_CreditFacilityDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="us-gaap_CreditFacilityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountLiability" xlink:label="us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountLiability" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoanOriginationCommitmentsMember" xlink:label="us-gaap_LoanOriginationCommitmentsMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StandbyLettersOfCreditMember" xlink:label="us-gaap_StandbyLettersOfCreditMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_UnusedLinesOfCreditMember" xlink:label="us-gaap_UnusedLinesOfCreditMember" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_CreditFacilityAxis" xlink:to="us-gaap_CreditFacilityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_UnusedLinesOfCreditMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="mbwm_OneToFourFamilyMortgagesMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ConsumerPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="mbwm_ConsumerOtherFinancingReceivable1Member" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_LoanOriginationCommitmentsMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_CreditFacilityAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CreditFacilityDomain" xlink:to="us-gaap_StandbyLettersOfCreditMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_CreditFacilityAxis" xlink:to="us-gaap_CreditFacilityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountLiability" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-10-fair-values-assets-and-liabilities-measured-at-fair-value-on-a-recurring-basis-details" xlink:href="mbwm-20190630.xsd#statement-note-10-fair-values-assets-and-liabilities-measured-at-fair-value-on-a-recurring-basis-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-10-fair-values-assets-and-liabilities-measured-at-fair-value-on-a-recurring-basis-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_MunicipalGeneralObligationBondsMember" xlink:label="mbwm_MunicipalGeneralObligationBondsMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_MunicipalRevenueBondsMember" xlink:label="mbwm_MunicipalRevenueBondsMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OtherDebtAndEquitySecuritiesMember" xlink:label="mbwm_OtherDebtAndEquitySecuritiesMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="us-gaap_FairValueMeasurementsRecurringMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MortgageBackedSecuritiesMember" xlink:label="us-gaap_MortgageBackedSecuritiesMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:label="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsRecurringMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_MortgageBackedSecuritiesMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_MunicipalGeneralObligationBondsMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_MunicipalRevenueBondsMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_OtherDebtAndEquitySecuritiesMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-10-fair-values-assets-and-liabilities-measured-at-fair-value-on-a-nonrecurring-basis-details" xlink:href="mbwm-20190630.xsd#statement-note-10-fair-values-assets-and-liabilities-measured-at-fair-value-on-a-nonrecurring-basis-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-10-fair-values-assets-and-liabilities-measured-at-fair-value-on-a-nonrecurring-basis-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_ForeclosedAssetsFairValueDisclosure" xlink:label="mbwm_ForeclosedAssetsFairValueDisclosure" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_ImpairedLoansFairValueDisclosure" xlink:label="mbwm_ImpairedLoansFairValueDisclosure" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AssetsFairValueDisclosure" xlink:label="us-gaap_AssetsFairValueDisclosure" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsNonrecurringMember" xlink:label="us-gaap_FairValueMeasurementsNonrecurringMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsNonrecurringMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_ImpairedLoansFairValueDisclosure" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_ForeclosedAssetsFairValueDisclosure" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AssetsFairValueDisclosure" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-2-securities-securities-in-a-continuous-loss-position-details" xlink:href="mbwm-20190630.xsd#statement-note-2-securities-securities-in-a-continuous-loss-position-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-2-securities-securities-in-a-continuous-loss-position-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_MunicipalGeneralObligationBondsMember" xlink:label="mbwm_MunicipalGeneralObligationBondsMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_MunicipalRevenueBondsMember" xlink:label="mbwm_MunicipalRevenueBondsMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OtherDebtAndEquitySecuritiesMember" xlink:label="mbwm_OtherDebtAndEquitySecuritiesMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MortgageBackedSecuritiesMember" xlink:label="us-gaap_MortgageBackedSecuritiesMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:label="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_MortgageBackedSecuritiesMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_MunicipalGeneralObligationBondsMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_MunicipalRevenueBondsMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_OtherDebtAndEquitySecuritiesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-age-analysis-of-past-due-loans-details" xlink:href="mbwm-20190630.xsd#statement-note-3-loans-and-allowance-for-loan-losses-age-analysis-of-past-due-loans-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-age-analysis-of-past-due-loans-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AcquiredLoanMember" xlink:label="mbwm_AcquiredLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_CommercialAndIndustrialMember" xlink:label="mbwm_CommercialAndIndustrialMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_HomeEquityAndOtherMember" xlink:label="mbwm_HomeEquityAndOtherMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OneToFourFamilyMortgagesMember" xlink:label="mbwm_OneToFourFamilyMortgagesMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OriginatedLoanMember" xlink:label="mbwm_OriginatedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:label="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RetailPortfolioSegmentMember" xlink:label="mbwm_RetailPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:label="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" xlink:label="us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentCurrent" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentCurrent" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDue" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentPastDue" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivables30To59DaysPastDueMember" xlink:label="us-gaap_FinancingReceivables30To59DaysPastDueMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivables60To89DaysPastDueMember" xlink:label="us-gaap_FinancingReceivables60To89DaysPastDueMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember" xlink:label="us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:label="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:to="us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="us-gaap_FinancingReceivables30To59DaysPastDueMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:to="us-gaap_FinancingReceivablesPeriodPastDueDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_OriginatedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_CommercialAndIndustrialMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_AcquiredLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="us-gaap_FinancingReceivables60To89DaysPastDueMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="mbwm_RetailPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_HomeEquityAndOtherMember" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_OneToFourFamilyMortgagesMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentPastDue" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentCurrent" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-loans-by-credit-quality-indicators-details" xlink:href="mbwm-20190630.xsd#statement-note-3-loans-and-allowance-for-loan-losses-loans-by-credit-quality-indicators-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-loans-by-credit-quality-indicators-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AcquiredLoanMember" xlink:label="mbwm_AcquiredLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_CommercialAndIndustrialMember" xlink:label="mbwm_CommercialAndIndustrialMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_Grades1To4Member" xlink:label="mbwm_Grades1To4Member" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_Grades5To7Member" xlink:label="mbwm_Grades5To7Member" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_Grades8To9Member" xlink:label="mbwm_Grades8To9Member" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OriginatedLoanMember" xlink:label="mbwm_OriginatedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:label="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:label="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InternalCreditAssessmentAxis" xlink:label="us-gaap_InternalCreditAssessmentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InternalCreditAssessmentDomain" xlink:label="us-gaap_InternalCreditAssessmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InternalCreditAssessmentDomain" xlink:label="us-gaap_InternalCreditAssessmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:label="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InternalCreditAssessmentAxis" xlink:to="us-gaap_InternalCreditAssessmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_InternalCreditAssessmentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="mbwm_Grades1To4Member" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_InternalCreditAssessmentAxis" xlink:to="us-gaap_InternalCreditAssessmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_CommercialAndIndustrialMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_OriginatedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_AcquiredLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="mbwm_Grades5To7Member" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="mbwm_Grades8To9Member" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-activity-in-allowance-for-loan-losses-and-the-recorded-investments-in-loans-details" xlink:href="mbwm-20190630.xsd#statement-note-3-loans-and-allowance-for-loan-losses-activity-in-allowance-for-loan-losses-and-the-recorded-investments-in-loans-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-activity-in-allowance-for-loan-losses-and-the-recorded-investments-in-loans-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AcquiredLoanMember" xlink:label="mbwm_AcquiredLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OriginatedLoanMember" xlink:label="mbwm_OriginatedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RetailPortfolioSegmentMember" xlink:label="mbwm_RetailPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLosses" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment" xlink:label="us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment" xlink:label="us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:label="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProvisionForLoanAndLeaseLosses" xlink:label="us-gaap_ProvisionForLoanAndLeaseLosses" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_UnallocatedFinancingReceivablesMember" xlink:label="us-gaap_UnallocatedFinancingReceivablesMember" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_OriginatedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_AcquiredLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="mbwm_RetailPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_UnallocatedFinancingReceivablesMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableAllowanceForCreditLosses" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ProvisionForLoanAndLeaseLosses" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-loans-modified-as-troubled-debt-restructurings-details" xlink:href="mbwm-20190630.xsd#statement-note-3-loans-and-allowance-for-loan-losses-loans-modified-as-troubled-debt-restructurings-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-loans-modified-as-troubled-debt-restructurings-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AcquiredLoanMember" xlink:label="mbwm_AcquiredLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_CommercialAndIndustrialMember" xlink:label="mbwm_CommercialAndIndustrialMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_HomeEquityAndOtherMember" xlink:label="mbwm_HomeEquityAndOtherMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OneToFourFamilyMortgagesMember" xlink:label="mbwm_OneToFourFamilyMortgagesMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OriginatedLoanMember" xlink:label="mbwm_OriginatedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:label="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RetailPortfolioSegmentMember" xlink:label="mbwm_RetailPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:label="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableModificationsNumberOfContracts2" xlink:label="us-gaap_FinancingReceivableModificationsNumberOfContracts2" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2" xlink:label="us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2" xlink:label="us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_OriginatedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_CommercialAndIndustrialMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="mbwm_RetailPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_HomeEquityAndOtherMember" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_OneToFourFamilyMortgagesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_AcquiredLoanMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableModificationsNumberOfContracts2" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-activity-for-troubled-debt-restructurings-details" xlink:href="mbwm-20190630.xsd#statement-note-3-loans-and-allowance-for-loan-losses-activity-for-troubled-debt-restructurings-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-activity-for-troubled-debt-restructurings-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AcquiredLoanMember" xlink:label="mbwm_AcquiredLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_CommercialAndIndustrialMember" xlink:label="mbwm_CommercialAndIndustrialMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_FinancingReceivableModifiedAsTroubledDebtRestructuringsAdditions" xlink:label="mbwm_FinancingReceivableModifiedAsTroubledDebtRestructuringsAdditions" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_FinancingReceivableModifiedAsTroubledDebtRestructuringsChargeOffs" xlink:label="mbwm_FinancingReceivableModifiedAsTroubledDebtRestructuringsChargeOffs" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_FinancingReceivableModifiedAsTroubledDebtRestructuringsPayments" xlink:label="mbwm_FinancingReceivableModifiedAsTroubledDebtRestructuringsPayments" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_FinancingReceivableModifiedAsTroubledDebtRestructuringsTransferToOtherRealEstate" xlink:label="mbwm_FinancingReceivableModifiedAsTroubledDebtRestructuringsTransferToOtherRealEstate" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_HomeEquityAndOtherMember" xlink:label="mbwm_HomeEquityAndOtherMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OneToFourFamilyMortgagesMember" xlink:label="mbwm_OneToFourFamilyMortgagesMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OriginatedLoanMember" xlink:label="mbwm_OriginatedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:label="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RetailPortfolioSegmentMember" xlink:label="mbwm_RetailPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:label="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableModificationsRecordedInvestment" xlink:label="us-gaap_FinancingReceivableModificationsRecordedInvestment" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_OriginatedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_CommercialAndIndustrialMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="mbwm_RetailPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_HomeEquityAndOtherMember" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_OneToFourFamilyMortgagesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_AcquiredLoanMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FinancingReceivableModificationsRecordedInvestment" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_FinancingReceivableModifiedAsTroubledDebtRestructuringsChargeOffs" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_FinancingReceivableModifiedAsTroubledDebtRestructuringsPayments" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_FinancingReceivableModifiedAsTroubledDebtRestructuringsTransferToOtherRealEstate" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_FinancingReceivableModifiedAsTroubledDebtRestructuringsAdditions" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-allowance-related-to-troubled-debt-restructurings-details" xlink:href="mbwm-20190630.xsd#statement-note-3-loans-and-allowance-for-loan-losses-allowance-related-to-troubled-debt-restructurings-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-allowance-related-to-troubled-debt-restructurings-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AllowanceForCreditLossesTroubledDebtRestructuring" xlink:label="mbwm_AllowanceForCreditLossesTroubledDebtRestructuring" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_CommercialAndIndustrialMember" xlink:label="mbwm_CommercialAndIndustrialMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_HomeEquityAndOtherMember" xlink:label="mbwm_HomeEquityAndOtherMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OneToFourFamilyMortgagesMember" xlink:label="mbwm_OneToFourFamilyMortgagesMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:label="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RetailPortfolioSegmentMember" xlink:label="mbwm_RetailPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:label="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_CommercialAndIndustrialMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="mbwm_RetailPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_HomeEquityAndOtherMember" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_OneToFourFamilyMortgagesMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_AllowanceForCreditLossesTroubledDebtRestructuring" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-5-deposits-summary-of-deposits-details" xlink:href="mbwm-20190630.xsd#statement-note-5-deposits-summary-of-deposits-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-5-deposits-summary-of-deposits-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AggregateIncreaseDecreaseInPercentageOfDeposits" xlink:label="mbwm_AggregateIncreaseDecreaseInPercentageOfDeposits" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AggregateLocalDepositLiabilities" xlink:label="mbwm_AggregateLocalDepositLiabilities" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AggregateOutOfAreaTimeDeposits" xlink:label="mbwm_AggregateOutOfAreaTimeDeposits" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AggregatePercentageIncreaseDecreaseInLocalDeposits" xlink:label="mbwm_AggregatePercentageIncreaseDecreaseInLocalDeposits" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AggregatePercentageIncreaseDecreaseInOutOfAreaDeposits" xlink:label="mbwm_AggregatePercentageIncreaseDecreaseInOutOfAreaDeposits" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AggregatePercentageOfDeposits" xlink:label="mbwm_AggregatePercentageOfDeposits" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AggregatePercentageOfLocalDeposits" xlink:label="mbwm_AggregatePercentageOfLocalDeposits" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AggregatePercentageOfOutOfAreaDeposits" xlink:label="mbwm_AggregatePercentageOfOutOfAreaDeposits" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OutOfAreaTimeDeposits100000AndOver" xlink:label="mbwm_OutOfAreaTimeDeposits100000AndOver" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OutOfAreaTimeDepositsUnder100000" xlink:label="mbwm_OutOfAreaTimeDepositsUnder100000" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_PercentageOfDomesticTimeDeposits100000AndOver" xlink:label="mbwm_PercentageOfDomesticTimeDeposits100000AndOver" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_PercentageOfDomesticTimeDepositsUnder100000" xlink:label="mbwm_PercentageOfDomesticTimeDepositsUnder100000" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_PercentageOfIncreaseDecreaseInDomesticTimeDeposits100000AndOver" xlink:label="mbwm_PercentageOfIncreaseDecreaseInDomesticTimeDeposits100000AndOver" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_PercentageOfIncreaseDecreaseInDomesticTimeDepositsUnder100000" xlink:label="mbwm_PercentageOfIncreaseDecreaseInDomesticTimeDepositsUnder100000" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_PercentageOfIncreaseDecreaseInMoneyMarketDeposits" xlink:label="mbwm_PercentageOfIncreaseDecreaseInMoneyMarketDeposits" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_PercentageOfIncreaseDecreaseInNonInterestBearingDemandDeposits" xlink:label="mbwm_PercentageOfIncreaseDecreaseInNonInterestBearingDemandDeposits" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_PercentageOfIncreaseDecreaseInOutOfAreaTime100000AndOver" xlink:label="mbwm_PercentageOfIncreaseDecreaseInOutOfAreaTime100000AndOver" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_PercentageOfIncreaseDecreaseInOutOfAreaTimeUnder100000" xlink:label="mbwm_PercentageOfIncreaseDecreaseInOutOfAreaTimeUnder100000" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_PercentageOfIncreaseDecreaseOfInterestBearingCheckingDeposits" xlink:label="mbwm_PercentageOfIncreaseDecreaseOfInterestBearingCheckingDeposits" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_PercentageOfIncreaseOrDecreaseOfSavingsDeposits" xlink:label="mbwm_PercentageOfIncreaseOrDecreaseOfSavingsDeposits" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_PercentageOfNonInterestBearingDomesticDepositsToDepositsDemand" xlink:label="mbwm_PercentageOfNonInterestBearingDomesticDepositsToDepositsDemand" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_PercentageOfOutOfAreaTimeDepositUnder100000" xlink:label="mbwm_PercentageOfOutOfAreaTimeDepositUnder100000" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_PercentageOfOutOfAreaTimeDeposits100000AndOver" xlink:label="mbwm_PercentageOfOutOfAreaTimeDeposits100000AndOver" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Deposits" xlink:label="us-gaap_Deposits" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestBearingDomesticDepositChecking" xlink:label="us-gaap_InterestBearingDomesticDepositChecking" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestBearingDomesticDepositMoneyMarket" xlink:label="us-gaap_InterestBearingDomesticDepositMoneyMarket" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InterestBearingDomesticDepositSavings" xlink:label="us-gaap_InterestBearingDomesticDepositSavings" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NoninterestBearingDomesticDepositDemand" xlink:label="us-gaap_NoninterestBearingDomesticDepositDemand" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PercentageOfInterestBearingDomesticDepositsToDepositsChecking" xlink:label="us-gaap_PercentageOfInterestBearingDomesticDepositsToDepositsChecking" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PercentageOfInterestBearingDomesticDepositsToDepositsMoneyMarket" xlink:label="us-gaap_PercentageOfInterestBearingDomesticDepositsToDepositsMoneyMarket" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PercentageOfInterestBearingDomesticDepositsToDepositsSavings" xlink:label="us-gaap_PercentageOfInterestBearingDomesticDepositsToDepositsSavings" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TimeDeposits100000OrMore" xlink:label="us-gaap_TimeDeposits100000OrMore" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TimeDepositsLessThan100000" xlink:label="us-gaap_TimeDepositsLessThan100000" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NoninterestBearingDomesticDepositDemand" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_PercentageOfNonInterestBearingDomesticDepositsToDepositsDemand" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_PercentageOfIncreaseDecreaseInNonInterestBearingDemandDeposits" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InterestBearingDomesticDepositChecking" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PercentageOfInterestBearingDomesticDepositsToDepositsChecking" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_PercentageOfIncreaseDecreaseOfInterestBearingCheckingDeposits" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InterestBearingDomesticDepositMoneyMarket" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PercentageOfInterestBearingDomesticDepositsToDepositsMoneyMarket" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_PercentageOfIncreaseDecreaseInMoneyMarketDeposits" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InterestBearingDomesticDepositSavings" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PercentageOfInterestBearingDomesticDepositsToDepositsSavings" xlink:type="arc"/>
    <link:definitionArc order="12" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_PercentageOfIncreaseOrDecreaseOfSavingsDeposits" xlink:type="arc"/>
    <link:definitionArc order="13" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TimeDepositsLessThan100000" xlink:type="arc"/>
    <link:definitionArc order="14" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_PercentageOfDomesticTimeDepositsUnder100000" xlink:type="arc"/>
    <link:definitionArc order="15" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_PercentageOfIncreaseDecreaseInDomesticTimeDepositsUnder100000" xlink:type="arc"/>
    <link:definitionArc order="16" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TimeDeposits100000OrMore" xlink:type="arc"/>
    <link:definitionArc order="17" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_PercentageOfDomesticTimeDeposits100000AndOver" xlink:type="arc"/>
    <link:definitionArc order="18" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_PercentageOfIncreaseDecreaseInDomesticTimeDeposits100000AndOver" xlink:type="arc"/>
    <link:definitionArc order="19" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_AggregateLocalDepositLiabilities" xlink:type="arc"/>
    <link:definitionArc order="20" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_AggregatePercentageOfLocalDeposits" xlink:type="arc"/>
    <link:definitionArc order="21" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_AggregatePercentageIncreaseDecreaseInLocalDeposits" xlink:type="arc"/>
    <link:definitionArc order="22" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_OutOfAreaTimeDepositsUnder100000" xlink:type="arc"/>
    <link:definitionArc order="23" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_PercentageOfOutOfAreaTimeDepositUnder100000" xlink:type="arc"/>
    <link:definitionArc order="24" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_PercentageOfIncreaseDecreaseInOutOfAreaTimeUnder100000" xlink:type="arc"/>
    <link:definitionArc order="25" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_OutOfAreaTimeDeposits100000AndOver" xlink:type="arc"/>
    <link:definitionArc order="26" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_PercentageOfOutOfAreaTimeDeposits100000AndOver" xlink:type="arc"/>
    <link:definitionArc order="27" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_PercentageOfIncreaseDecreaseInOutOfAreaTime100000AndOver" xlink:type="arc"/>
    <link:definitionArc order="28" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_AggregateOutOfAreaTimeDeposits" xlink:type="arc"/>
    <link:definitionArc order="29" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_AggregatePercentageOfOutOfAreaDeposits" xlink:type="arc"/>
    <link:definitionArc order="30" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_AggregatePercentageIncreaseDecreaseInOutOfAreaDeposits" xlink:type="arc"/>
    <link:definitionArc order="31" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_Deposits" xlink:type="arc"/>
    <link:definitionArc order="32" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_AggregatePercentageOfDeposits" xlink:type="arc"/>
    <link:definitionArc order="33" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_AggregateIncreaseDecreaseInPercentageOfDeposits" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-impaired-loans-details" xlink:href="mbwm-20190630.xsd#statement-note-3-loans-and-allowance-for-loan-losses-impaired-loans-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-impaired-loans-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AcquiredLoanMember" xlink:label="mbwm_AcquiredLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_CommercialAndIndustrialMember" xlink:label="mbwm_CommercialAndIndustrialMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_HomeEquityAndOtherMember" xlink:label="mbwm_HomeEquityAndOtherMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OneToFourFamilyMortgagesMember" xlink:label="mbwm_OneToFourFamilyMortgagesMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OriginatedLoanMember" xlink:label="mbwm_OriginatedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:label="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RetailPortfolioSegmentMember" xlink:label="mbwm_RetailPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:label="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment" xlink:label="us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ImpairedFinancingReceivableRecordedInvestment" xlink:label="us-gaap_ImpairedFinancingReceivableRecordedInvestment" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ImpairedFinancingReceivableRelatedAllowance" xlink:label="us-gaap_ImpairedFinancingReceivableRelatedAllowance" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance" xlink:label="us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment" xlink:label="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment" xlink:label="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance" xlink:label="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment" xlink:label="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment" xlink:label="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance" xlink:label="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_OriginatedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_CommercialAndIndustrialMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_AcquiredLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="mbwm_RetailPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_HomeEquityAndOtherMember" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_OneToFourFamilyMortgagesMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableRelatedAllowance" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableRecordedInvestment" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-11-regulatory-matters-actual-capital-levels-and-minimum-levels-details" xlink:href="mbwm-20190630.xsd#statement-note-11-regulatory-matters-actual-capital-levels-and-minimum-levels-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-11-regulatory-matters-actual-capital-levels-and-minimum-levels-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_BankMember" xlink:label="mbwm_BankMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_CommonEquityTier1RiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets" xlink:label="mbwm_CommonEquityTier1RiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_CommonEquityTier1RiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" xlink:label="mbwm_CommonEquityTier1RiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="srt_ConsolidatedEntitiesAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Capital" xlink:label="us-gaap_Capital" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CapitalRequiredForCapitalAdequacy" xlink:label="us-gaap_CapitalRequiredForCapitalAdequacy" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets" xlink:label="us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CapitalRequiredToBeWellCapitalized" xlink:label="us-gaap_CapitalRequiredToBeWellCapitalized" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" xlink:label="us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CapitalToRiskWeightedAssets" xlink:label="us-gaap_CapitalToRiskWeightedAssets" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonEquityTierOneCapital" xlink:label="us-gaap_CommonEquityTierOneCapital" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonEquityTierOneCapitalRatio" xlink:label="us-gaap_CommonEquityTierOneCapitalRatio" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonEquityTierOneCapitalRequiredForCapitalAdequacy" xlink:label="us-gaap_CommonEquityTierOneCapitalRequiredForCapitalAdequacy" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonEquityTierOneCapitalRequiredToBeWellCapitalized" xlink:label="us-gaap_CommonEquityTierOneCapitalRequiredToBeWellCapitalized" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConsolidatedEntitiesMember" xlink:label="us-gaap_ConsolidatedEntitiesMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TierOneLeverageCapital" xlink:label="us-gaap_TierOneLeverageCapital" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy" xlink:label="us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets" xlink:label="us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized" xlink:label="us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets" xlink:label="us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TierOneLeverageCapitalToAverageAssets" xlink:label="us-gaap_TierOneLeverageCapitalToAverageAssets" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TierOneRiskBasedCapital" xlink:label="us-gaap_TierOneRiskBasedCapital" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy" xlink:label="us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets" xlink:label="us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized" xlink:label="us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" xlink:label="us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets" xlink:label="us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_ConsolidatedEntitiesAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="us-gaap_ConsolidatedEntitiesMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="mbwm_BankMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_Capital" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CapitalToRiskWeightedAssets" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CapitalRequiredForCapitalAdequacy" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CapitalRequiredToBeWellCapitalized" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TierOneRiskBasedCapital" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized" xlink:type="arc"/>
    <link:definitionArc order="12" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" xlink:type="arc"/>
    <link:definitionArc order="13" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonEquityTierOneCapital" xlink:type="arc"/>
    <link:definitionArc order="14" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonEquityTierOneCapitalRatio" xlink:type="arc"/>
    <link:definitionArc order="15" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonEquityTierOneCapitalRequiredForCapitalAdequacy" xlink:type="arc"/>
    <link:definitionArc order="16" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_CommonEquityTier1RiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets" xlink:type="arc"/>
    <link:definitionArc order="17" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonEquityTierOneCapitalRequiredToBeWellCapitalized" xlink:type="arc"/>
    <link:definitionArc order="18" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_CommonEquityTier1RiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" xlink:type="arc"/>
    <link:definitionArc order="19" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TierOneLeverageCapital" xlink:type="arc"/>
    <link:definitionArc order="20" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TierOneLeverageCapitalToAverageAssets" xlink:type="arc"/>
    <link:definitionArc order="21" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy" xlink:type="arc"/>
    <link:definitionArc order="22" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets" xlink:type="arc"/>
    <link:definitionArc order="23" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized" xlink:type="arc"/>
    <link:definitionArc order="24" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-9-fair-values-of-financial-instruments-fair-value-hierarchy-of-financial-instruments-details" xlink:href="mbwm-20190630.xsd#statement-note-9-fair-values-of-financial-instruments-fair-value-hierarchy-of-financial-instruments-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-9-fair-values-of-financial-instruments-fair-value-hierarchy-of-financial-instruments-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AccruedInterestPayableFairValueDisclosure" xlink:label="mbwm_AccruedInterestPayableFairValueDisclosure" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AccruedInterestReceivableFairValueDisclosure" xlink:label="mbwm_AccruedInterestReceivableFairValueDisclosure" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_CashFairValueDisclosure" xlink:label="mbwm_CashFairValueDisclosure" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:label="us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:label="us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DepositsFairValueDisclosure" xlink:label="us-gaap_DepositsFairValueDisclosure" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="us-gaap_FairValueByMeasurementBasisAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FederalHomeLoanBankBorrowingsFairValueDisclosure" xlink:label="us-gaap_FederalHomeLoanBankBorrowingsFairValueDisclosure" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InvestmentInFederalHomeLoanBankStockFairValueDisclosure" xlink:label="us-gaap_InvestmentInFederalHomeLoanBankStockFairValueDisclosure" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansHeldForSaleFairValueDisclosure" xlink:label="us-gaap_LoansHeldForSaleFairValueDisclosure" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansReceivableFairValueDisclosure" xlink:label="us-gaap_LoansReceivableFairValueDisclosure" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure" xlink:label="us-gaap_SecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ServicingAssetAtFairValueAmount" xlink:label="us-gaap_ServicingAssetAtFairValueAmount" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByMeasurementBasisAxis" xlink:to="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FairValueByMeasurementBasisAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:to="us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByMeasurementBasisAxis" xlink:to="us-gaap_PortionAtFairValueFairValueDisclosureMember-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:to="us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_CashFairValueDisclosure" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InvestmentInFederalHomeLoanBankStockFairValueDisclosure" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LoansReceivableFairValueDisclosure" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LoansHeldForSaleFairValueDisclosure" xlink:type="arc"/>
    <link:definitionArc order="7" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ServicingAssetAtFairValueAmount" xlink:type="arc"/>
    <link:definitionArc order="8" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_AccruedInterestReceivableFairValueDisclosure" xlink:type="arc"/>
    <link:definitionArc order="9" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DepositsFairValueDisclosure" xlink:type="arc"/>
    <link:definitionArc order="10" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure" xlink:type="arc"/>
    <link:definitionArc order="11" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FederalHomeLoanBankBorrowingsFairValueDisclosure" xlink:type="arc"/>
    <link:definitionArc order="12" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations" xlink:type="arc"/>
    <link:definitionArc order="13" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_AccruedInterestPayableFairValueDisclosure" xlink:type="arc"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-components-of-loan-portfolio-details" xlink:href="mbwm-20190630.xsd#statement-note-3-loans-and-allowance-for-loan-losses-components-of-loan-portfolio-details" xlink:type="simple"/>
  <link:definitionLink xlink:role="http://www.mercbank.com/20190630/role/statement-note-3-loans-and-allowance-for-loan-losses-components-of-loan-portfolio-details" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_AcquiredLoanMember" xlink:label="mbwm_AcquiredLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_CommercialAndIndustrialMember" xlink:label="mbwm_CommercialAndIndustrialMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_HomeEquityAndOtherMember" xlink:label="mbwm_HomeEquityAndOtherMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_LoanPortfolioClassesAndSegmentsAsPercentageOfAggregateLoan" xlink:label="mbwm_LoanPortfolioClassesAndSegmentsAsPercentageOfAggregateLoan" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_LoansAndLeasesReceivableNetOfDeferredIncomeIncreaseDecreasePercentage" xlink:label="mbwm_LoansAndLeasesReceivableNetOfDeferredIncomeIncreaseDecreasePercentage" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OneToFourFamilyMortgagesMember" xlink:label="mbwm_OneToFourFamilyMortgagesMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_OriginatedLoanMember" xlink:label="mbwm_OriginatedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:label="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RealEstateOwnerOccupiedLoanMember" xlink:label="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_RetailPortfolioSegmentMember" xlink:label="mbwm_RetailPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="mbwm-20190630.xsd#mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:label="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:label="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator"/>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="locator"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancialInstrumentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_OriginatedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain-default" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_CommercialAndIndustrialMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain-default" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="mbwm_AcquiredLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_VacantLandAndLandDevelopmentAndResidentialConstructionLoanMember" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateNonOwnerOccupiedLoanMember" xlink:type="arc"/>
    <link:definitionArc order="4" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_RealEstateMultiFamilyAndResidentialRentalLoanMember" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="mbwm_RetailPortfolioSegmentMember" xlink:type="arc"/>
    <link:definitionArc order="5" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_HomeEquityAndOtherMember" xlink:type="arc"/>
    <link:definitionArc order="6" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="mbwm_OneToFourFamilyMortgagesMember" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain-default" xlink:type="arc"/>
    <link:definitionArc order="0" xbrldt:closed="true" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" xlink:type="arc"/>
    <link:definitionArc order="1" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="arc"/>
    <link:definitionArc order="2" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_LoanPortfolioClassesAndSegmentsAsPercentageOfAggregateLoan" xlink:type="arc"/>
    <link:definitionArc order="3" xbrldt:closed="true" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="mbwm_LoansAndLeasesReceivableNetOfDeferredIncomeIncreaseDecreasePercentage" xlink:type="arc"/>
  </link:definitionLink>
</link:linkbase>
