<?xml version="1.0" encoding="us-ascii"?>
<!--Generated by EDGARfilings PROfile 4.3.3.1 Broadridge-->
<link:linkbase 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" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:t1="http://xbrl.org/2005/xbrldt">
  <link:roleRef roleURI="http://communitybankna.com/role/SegmentInformationDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#SegmentInformationDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/DerivativeInstrumentsDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#DerivativeInstrumentsDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/FairValueCarryingAmountsAndEstimatedFairValuesOfOtherFinancialInstrumentsDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#FairValueCarryingAmountsAndEstimatedFairValuesOfOtherFinancialInstrumentsDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/FairValueSignificantUnobservableInputsDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#FairValueSignificantUnobservableInputsDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/FairValueAssetsAndLiabilitiesMeasuredOnNonrecurringBasisDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#FairValueAssetsAndLiabilitiesMeasuredOnNonrecurringBasisDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/FairValueFinancialAssetsAndLiabilitiesAccountedForAtFairValueOnRecurringBasisDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#FairValueFinancialAssetsAndLiabilitiesAccountedForAtFairValueOnRecurringBasisDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/CommitmentsContingentLiabilitiesAndRestrictionsDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#CommitmentsContingentLiabilitiesAndRestrictionsDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/EarningsPerShareDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#EarningsPerShareDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/BenefitPlansDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#BenefitPlansDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/MandatorilyRedeemablePreferredSecuritiesDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#MandatorilyRedeemablePreferredSecuritiesDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/GoodwillAndIdentifiableIntangibleAssetsDetailsCalc2" xlink:type="simple" xlink:href="cbu-20180630.xsd#GoodwillAndIdentifiableIntangibleAssetsDetailsCalc2" />
  <link:roleRef roleURI="http://communitybankna.com/role/GoodwillAndIdentifiableIntangibleAssetsDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#GoodwillAndIdentifiableIntangibleAssetsDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/LoansAllowanceForLoanLossesDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#LoansAllowanceForLoanLossesDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/LoansTroubledDebtRestructuringsTdrsDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#LoansTroubledDebtRestructuringsTdrsDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/LoansSummaryOfImpairedLoansExcludingPurchasedImpairedDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#LoansSummaryOfImpairedLoansExcludingPurchasedImpairedDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/LoansAmountOfBusinessLendingLoansByCreditQualityCategoryDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#LoansAmountOfBusinessLendingLoansByCreditQualityCategoryDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/LoansCreditQualityByPastDueStatusDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#LoansCreditQualityByPastDueStatusDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/LoansLoanSummaryDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#LoansLoanSummaryDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/InvestmentSecuritiesAmortizedCostAndEstimatedFairValueOfDebtSecuritiesByContractualMaturityDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#InvestmentSecuritiesAmortizedCostAndEstimatedFairValueOfDebtSecuritiesByContractualMaturityDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/InvestmentSecuritiesInvestmentSecuritiesInContinuousUnrealizedLossPositionDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#InvestmentSecuritiesInvestmentSecuritiesInContinuousUnrealizedLossPositionDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/InvestmentSecuritiesEquityAndOtherSecuritiesDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#InvestmentSecuritiesEquityAndOtherSecuritiesDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/InvestmentSecuritiesAvailableforsalePortfolioDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#InvestmentSecuritiesAvailableforsalePortfolioDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/AccountingPoliciesDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#AccountingPoliciesDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/AcquisitionsIntangibleAssetGoodwillAndAcquisitionrelatedExpensesDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#AcquisitionsIntangibleAssetGoodwillAndAcquisitionrelatedExpensesDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/AcquisitionsSummaryOfLoansAcquiredDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#AcquisitionsSummaryOfLoansAcquiredDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/AcquisitionsEstimatedFairValueOfAssetsAcquiredAndLiabilitiesAssumedDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#AcquisitionsEstimatedFairValueOfAssetsAcquiredAndLiabilitiesAssumedDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/AcquisitionsDetails" xlink:type="simple" xlink:href="cbu-20180630.xsd#AcquisitionsDetails" />
  <link:roleRef roleURI="http://communitybankna.com/role/SegmentInformationTables" xlink:type="simple" xlink:href="cbu-20180630.xsd#SegmentInformationTables" />
  <link:roleRef roleURI="http://communitybankna.com/role/FairValueTables" xlink:type="simple" xlink:href="cbu-20180630.xsd#FairValueTables" />
  <link:roleRef roleURI="http://communitybankna.com/role/CommitmentsContingentLiabilitiesAndRestrictionsTables" xlink:type="simple" xlink:href="cbu-20180630.xsd#CommitmentsContingentLiabilitiesAndRestrictionsTables" />
  <link:roleRef roleURI="http://communitybankna.com/role/EarningsPerShareTables" xlink:type="simple" xlink:href="cbu-20180630.xsd#EarningsPerShareTables" />
  <link:roleRef roleURI="http://communitybankna.com/role/BenefitPlansTables" xlink:type="simple" xlink:href="cbu-20180630.xsd#BenefitPlansTables" />
  <link:roleRef roleURI="http://communitybankna.com/role/MandatorilyRedeemablePreferredSecuritiesTables" xlink:type="simple" xlink:href="cbu-20180630.xsd#MandatorilyRedeemablePreferredSecuritiesTables" />
  <link:roleRef roleURI="http://communitybankna.com/role/GoodwillAndIdentifiableIntangibleAssetsTables" xlink:type="simple" xlink:href="cbu-20180630.xsd#GoodwillAndIdentifiableIntangibleAssetsTables" />
  <link:roleRef roleURI="http://communitybankna.com/role/LoansTables" xlink:type="simple" xlink:href="cbu-20180630.xsd#LoansTables" />
  <link:roleRef roleURI="http://communitybankna.com/role/InvestmentSecuritiesTables" xlink:type="simple" xlink:href="cbu-20180630.xsd#InvestmentSecuritiesTables" />
  <link:roleRef roleURI="http://communitybankna.com/role/AcquisitionsTables" xlink:type="simple" xlink:href="cbu-20180630.xsd#AcquisitionsTables" />
  <link:roleRef roleURI="http://communitybankna.com/role/AccountingPoliciesPolicies" xlink:type="simple" xlink:href="cbu-20180630.xsd#AccountingPoliciesPolicies" />
  <link:roleRef roleURI="http://communitybankna.com/role/BasisOfPresentationPolicies" xlink:type="simple" xlink:href="cbu-20180630.xsd#BasisOfPresentationPolicies" />
  <link:roleRef roleURI="http://communitybankna.com/role/SegmentInformation" xlink:type="simple" xlink:href="cbu-20180630.xsd#SegmentInformation" />
  <link:roleRef roleURI="http://communitybankna.com/role/DerivativeInstruments" xlink:type="simple" xlink:href="cbu-20180630.xsd#DerivativeInstruments" />
  <link:roleRef roleURI="http://communitybankna.com/role/FairValue" xlink:type="simple" xlink:href="cbu-20180630.xsd#FairValue" />
  <link:roleRef roleURI="http://communitybankna.com/role/CommitmentsContingentLiabilitiesAndRestrictions" xlink:type="simple" xlink:href="cbu-20180630.xsd#CommitmentsContingentLiabilitiesAndRestrictions" />
  <link:roleRef roleURI="http://communitybankna.com/role/EarningsPerShare" xlink:type="simple" xlink:href="cbu-20180630.xsd#EarningsPerShare" />
  <link:roleRef roleURI="http://communitybankna.com/role/BenefitPlans" xlink:type="simple" xlink:href="cbu-20180630.xsd#BenefitPlans" />
  <link:roleRef roleURI="http://communitybankna.com/role/MandatorilyRedeemablePreferredSecurities" xlink:type="simple" xlink:href="cbu-20180630.xsd#MandatorilyRedeemablePreferredSecurities" />
  <link:roleRef roleURI="http://communitybankna.com/role/GoodwillAndIdentifiableIntangibleAssets" xlink:type="simple" xlink:href="cbu-20180630.xsd#GoodwillAndIdentifiableIntangibleAssets" />
  <link:roleRef roleURI="http://communitybankna.com/role/Loans" xlink:type="simple" xlink:href="cbu-20180630.xsd#Loans" />
  <link:roleRef roleURI="http://communitybankna.com/role/InvestmentSecurities" xlink:type="simple" xlink:href="cbu-20180630.xsd#InvestmentSecurities" />
  <link:roleRef roleURI="http://communitybankna.com/role/AccountingPolicies" xlink:type="simple" xlink:href="cbu-20180630.xsd#AccountingPolicies" />
  <link:roleRef roleURI="http://communitybankna.com/role/Acquisitions" xlink:type="simple" xlink:href="cbu-20180630.xsd#Acquisitions" />
  <link:roleRef roleURI="http://communitybankna.com/role/BasisOfPresentation" xlink:type="simple" xlink:href="cbu-20180630.xsd#BasisOfPresentation" />
  <link:roleRef roleURI="http://communitybankna.com/role/ConsolidatedStatementsOfCashFlowsUnauditedParenthetical" xlink:type="simple" xlink:href="cbu-20180630.xsd#ConsolidatedStatementsOfCashFlowsUnauditedParenthetical" />
  <link:roleRef roleURI="http://communitybankna.com/role/ConsolidatedStatementsOfCashFlowsUnaudited" xlink:type="simple" xlink:href="cbu-20180630.xsd#ConsolidatedStatementsOfCashFlowsUnaudited" />
  <link:roleRef roleURI="http://communitybankna.com/role/ConsolidatedStatementOfChangesInShareholdersEquityUnauditedParenthetical" xlink:type="simple" xlink:href="cbu-20180630.xsd#ConsolidatedStatementOfChangesInShareholdersEquityUnauditedParenthetical" />
  <link:roleRef roleURI="http://communitybankna.com/role/ConsolidatedStatementOfChangesInShareholdersEquityUnaudited" xlink:type="simple" xlink:href="cbu-20180630.xsd#ConsolidatedStatementOfChangesInShareholdersEquityUnaudited" />
  <link:roleRef roleURI="http://communitybankna.com/role/ConsolidatedStatementsOfComprehensiveIncomeUnaudited" xlink:type="simple" xlink:href="cbu-20180630.xsd#ConsolidatedStatementsOfComprehensiveIncomeUnaudited" />
  <link:roleRef roleURI="http://communitybankna.com/role/ConsolidatedStatementsOfIncomeUnaudited" xlink:type="simple" xlink:href="cbu-20180630.xsd#ConsolidatedStatementsOfIncomeUnaudited" />
  <link:roleRef roleURI="http://communitybankna.com/role/ConsolidatedStatementsOfConditionUnauditedParenthetical" xlink:type="simple" xlink:href="cbu-20180630.xsd#ConsolidatedStatementsOfConditionUnauditedParenthetical" />
  <link:roleRef roleURI="http://communitybankna.com/role/ConsolidatedStatementsOfConditionUnaudited" xlink:type="simple" xlink:href="cbu-20180630.xsd#ConsolidatedStatementsOfConditionUnaudited" />
  <link:roleRef roleURI="http://communitybankna.com/role/DocumentAndEntityInformation" xlink:type="simple" xlink:href="cbu-20180630.xsd#DocumentAndEntityInformation" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/DocumentAndEntityInformation" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/ConsolidatedStatementsOfConditionUnaudited" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/ConsolidatedStatementsOfConditionUnauditedParenthetical" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/ConsolidatedStatementsOfIncomeUnaudited" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/ConsolidatedStatementsOfComprehensiveIncomeUnaudited" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/ConsolidatedStatementOfChangesInShareholdersEquityUnaudited">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StatementLineItems" xlink:label="StatementLineItems" xlink:title="StatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:label="IncreaseDecreaseInStockholdersEquityRollForward" xlink:title="IncreaseDecreaseInStockholdersEquityRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInStockholdersEquityRollForward" xlink:title="definition: StatementLineItems to IncreaseDecreaseInStockholdersEquityRollForward" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="StockholdersEquity" xlink:title="StockholdersEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockholdersEquity" xlink:title="definition: StatementLineItems to StockholdersEquity" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="CommonStockSharesOutstanding" xlink:title="CommonStockSharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CommonStockSharesOutstanding" xlink:title="definition: StatementLineItems to CommonStockSharesOutstanding" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="NetIncomeLoss" xlink:title="NetIncomeLoss" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="NetIncomeLoss" xlink:title="definition: StatementLineItems to NetIncomeLoss" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_OtherComprehensiveIncomeLossNetOfTaxBeforeCumulativeEffectOfChangeInAccountingPrinciplePortionAttributableToParent" xlink:label="OtherComprehensiveIncomeLossNetOfTaxBeforeCumulativeEffectOfChangeInAccountingPrinciplePortionAttributableToParent" xlink:title="OtherComprehensiveIncomeLossNetOfTaxBeforeCumulativeEffectOfChangeInAccountingPrinciplePortionAttributableToParent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="OtherComprehensiveIncomeLossNetOfTaxBeforeCumulativeEffectOfChangeInAccountingPrinciplePortionAttributableToParent" xlink:title="definition: StatementLineItems to OtherComprehensiveIncomeLossNetOfTaxBeforeCumulativeEffectOfChangeInAccountingPrinciplePortionAttributableToParent" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" xlink:label="CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" xlink:title="CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" xlink:title="definition: StatementLineItems to CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DividendsAbstract" xlink:label="DividendsAbstract" xlink:title="DividendsAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="DividendsAbstract" xlink:title="definition: StatementLineItems to DividendsAbstract" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockOwnershipPlan" xlink:label="StockIssuedDuringPeriodValueEmployeeStockOwnershipPlan" xlink:title="StockIssuedDuringPeriodValueEmployeeStockOwnershipPlan" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodValueEmployeeStockOwnershipPlan" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodValueEmployeeStockOwnershipPlan" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockOwnershipPlan" xlink:label="StockIssuedDuringPeriodSharesEmployeeStockOwnershipPlan" xlink:title="StockIssuedDuringPeriodSharesEmployeeStockOwnershipPlan" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesEmployeeStockOwnershipPlan" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesEmployeeStockOwnershipPlan" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:title="AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:title="definition: StatementLineItems to AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_StockIssuedDuringPeriodValueDeferredCompensationArrangements" xlink:label="StockIssuedDuringPeriodValueDeferredCompensationArrangements" xlink:title="StockIssuedDuringPeriodValueDeferredCompensationArrangements" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodValueDeferredCompensationArrangements" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodValueDeferredCompensationArrangements" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_StockIssuedDuringPeriodSharesDeferredCompensationArrangements" xlink:label="StockIssuedDuringPeriodSharesDeferredCompensationArrangements" xlink:title="StockIssuedDuringPeriodSharesDeferredCompensationArrangements" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesDeferredCompensationArrangements" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesDeferredCompensationArrangements" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued" xlink:label="StockIssuedDuringPeriodValueTreasuryStockReissued" xlink:title="StockIssuedDuringPeriodValueTreasuryStockReissued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodValueTreasuryStockReissued" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodValueTreasuryStockReissued" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued" xlink:label="StockIssuedDuringPeriodSharesTreasuryStockReissued" xlink:title="StockIssuedDuringPeriodSharesTreasuryStockReissued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesTreasuryStockReissued" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesTreasuryStockReissued" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DividendsCommonStock" xlink:label="DividendsCommonStock" xlink:title="DividendsCommonStock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="DividendsCommonStock" xlink:title="definition: StatementLineItems to DividendsCommonStock" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StatementTable" xlink:label="StatementTable" xlink:title="StatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="StatementLineItems" xlink:to="StatementTable" xlink:title="definition: StatementLineItems to StatementTable" order="16.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="StatementTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: StatementTable to StatementEquityComponentsAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_2" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityComponentDomain to CommonStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="AdditionalPaidInCapitalMember" xlink:title="AdditionalPaidInCapitalMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="AdditionalPaidInCapitalMember" xlink:title="definition: EquityComponentDomain to AdditionalPaidInCapitalMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="RetainedEarningsMember" xlink:title="RetainedEarningsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="RetainedEarningsMember" xlink:title="definition: EquityComponentDomain to RetainedEarningsMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="AccumulatedOtherComprehensiveIncomeMember" xlink:title="AccumulatedOtherComprehensiveIncomeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="AccumulatedOtherComprehensiveIncomeMember" xlink:title="definition: EquityComponentDomain to AccumulatedOtherComprehensiveIncomeMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TreasuryStockMember" xlink:label="TreasuryStockMember" xlink:title="TreasuryStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="TreasuryStockMember" xlink:title="definition: EquityComponentDomain to TreasuryStockMember" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DeferredCompensationShareBasedPaymentsMember" xlink:label="DeferredCompensationShareBasedPaymentsMember" xlink:title="DeferredCompensationShareBasedPaymentsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="DeferredCompensationShareBasedPaymentsMember" xlink:title="definition: EquityComponentDomain to DeferredCompensationShareBasedPaymentsMember" order="6.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/ConsolidatedStatementOfChangesInShareholdersEquityUnauditedParenthetical" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/ConsolidatedStatementsOfCashFlowsUnaudited" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/ConsolidatedStatementsOfCashFlowsUnauditedParenthetical" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/BasisOfPresentation" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/Acquisitions" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/AccountingPolicies" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/InvestmentSecurities" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/Loans" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/GoodwillAndIdentifiableIntangibleAssets" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/MandatorilyRedeemablePreferredSecurities" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/BenefitPlans" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/EarningsPerShare" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/CommitmentsContingentLiabilitiesAndRestrictions" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/FairValue" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/DerivativeInstruments" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/SegmentInformation" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/BasisOfPresentationPolicies" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/AccountingPoliciesPolicies" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/AcquisitionsTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/InvestmentSecuritiesTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/LoansTables">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LoansAndLeasesReceivableDisclosureLineItems" xlink:label="LoansAndLeasesReceivableDisclosureLineItems" xlink:title="LoansAndLeasesReceivableDisclosureLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock" xlink:label="ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock" xlink:title="ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LoansAndLeasesReceivableDisclosureLineItems" xlink:to="ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock" xlink:title="definition: LoansAndLeasesReceivableDisclosureLineItems to ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_ScheduleOfAccretableDiscountRelatedToCreditImpairedAcquiredLoansTableTextBlock" xlink:label="ScheduleOfAccretableDiscountRelatedToCreditImpairedAcquiredLoansTableTextBlock" xlink:title="ScheduleOfAccretableDiscountRelatedToCreditImpairedAcquiredLoansTableTextBlock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LoansAndLeasesReceivableDisclosureLineItems" xlink:to="ScheduleOfAccretableDiscountRelatedToCreditImpairedAcquiredLoansTableTextBlock" xlink:title="definition: LoansAndLeasesReceivableDisclosureLineItems to ScheduleOfAccretableDiscountRelatedToCreditImpairedAcquiredLoansTableTextBlock" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PastDueFinancingReceivablesTableTextBlock" xlink:label="PastDueFinancingReceivablesTableTextBlock" xlink:title="PastDueFinancingReceivablesTableTextBlock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LoansAndLeasesReceivableDisclosureLineItems" xlink:to="PastDueFinancingReceivablesTableTextBlock" xlink:title="definition: LoansAndLeasesReceivableDisclosureLineItems to PastDueFinancingReceivablesTableTextBlock" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableCreditQualityIndicatorsTableTextBlock" xlink:label="FinancingReceivableCreditQualityIndicatorsTableTextBlock" xlink:title="FinancingReceivableCreditQualityIndicatorsTableTextBlock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LoansAndLeasesReceivableDisclosureLineItems" xlink:to="FinancingReceivableCreditQualityIndicatorsTableTextBlock" xlink:title="definition: LoansAndLeasesReceivableDisclosureLineItems to FinancingReceivableCreditQualityIndicatorsTableTextBlock" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ImpairedFinancingReceivablesTableTextBlock" xlink:label="ImpairedFinancingReceivablesTableTextBlock" xlink:title="ImpairedFinancingReceivablesTableTextBlock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LoansAndLeasesReceivableDisclosureLineItems" xlink:to="ImpairedFinancingReceivablesTableTextBlock" xlink:title="definition: LoansAndLeasesReceivableDisclosureLineItems to ImpairedFinancingReceivablesTableTextBlock" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TroubledDebtRestructuringsOnFinancingReceivablesTableTextBlock" xlink:label="TroubledDebtRestructuringsOnFinancingReceivablesTableTextBlock" xlink:title="TroubledDebtRestructuringsOnFinancingReceivablesTableTextBlock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LoansAndLeasesReceivableDisclosureLineItems" xlink:to="TroubledDebtRestructuringsOnFinancingReceivablesTableTextBlock" xlink:title="definition: LoansAndLeasesReceivableDisclosureLineItems to TroubledDebtRestructuringsOnFinancingReceivablesTableTextBlock" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock" xlink:label="AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock" xlink:title="AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LoansAndLeasesReceivableDisclosureLineItems" xlink:to="AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock" xlink:title="definition: LoansAndLeasesReceivableDisclosureLineItems to AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LoansAndLeasesReceivableDisclosureTable" xlink:label="LoansAndLeasesReceivableDisclosureTable" xlink:title="LoansAndLeasesReceivableDisclosureTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="LoansAndLeasesReceivableDisclosureLineItems" xlink:to="LoansAndLeasesReceivableDisclosureTable" xlink:title="definition: LoansAndLeasesReceivableDisclosureLineItems to LoansAndLeasesReceivableDisclosureTable" order="8.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:title="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="LoansAndLeasesReceivableDisclosureTable" xlink:to="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:title="definition: LoansAndLeasesReceivableDisclosureTable to FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:title="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:title="definition: FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis to FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" xlink:title="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" xlink:title="definition: FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis to FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommercialLoanMember" xlink:label="CommercialLoanMember" xlink:title="CommercialLoanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="CommercialLoanMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to CommercialLoanMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_AllOtherLoansMember" xlink:label="AllOtherLoansMember" xlink:title="AllOtherLoansMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="AllOtherLoansMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to AllOtherLoansMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/GoodwillAndIdentifiableIntangibleAssetsTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/MandatorilyRedeemablePreferredSecuritiesTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/BenefitPlansTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/EarningsPerShareTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/CommitmentsContingentLiabilitiesAndRestrictionsTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/FairValueTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/SegmentInformationTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/AcquisitionsDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="BusinessAcquisitionLineItems" xlink:title="BusinessAcquisitionLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferredIncludingEquityInterestInAcquireeHeldPriorToCombinationAbstract" xlink:label="BusinessCombinationConsiderationTransferredIncludingEquityInterestInAcquireeHeldPriorToCombinationAbstract" xlink:title="BusinessCombinationConsiderationTransferredIncludingEquityInterestInAcquireeHeldPriorToCombinationAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationConsiderationTransferredIncludingEquityInterestInAcquireeHeldPriorToCombinationAbstract" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationConsiderationTransferredIncludingEquityInterestInAcquireeHeldPriorToCombinationAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferred1" xlink:label="BusinessCombinationConsiderationTransferred1" xlink:title="BusinessCombinationConsiderationTransferred1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationConsiderationTransferred1" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationConsiderationTransferred1" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired" xlink:label="PaymentsToAcquireBusinessesNetOfCashAcquired" xlink:title="PaymentsToAcquireBusinessesNetOfCashAcquired" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="PaymentsToAcquireBusinessesNetOfCashAcquired" xlink:title="definition: BusinessAcquisitionLineItems to PaymentsToAcquireBusinessesNetOfCashAcquired" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:label="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:title="definition: BusinessAcquisitionLineItems to BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_Goodwill" xlink:label="Goodwill" xlink:title="Goodwill" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="Goodwill" xlink:title="definition: BusinessAcquisitionLineItems to Goodwill" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_NumberOfBranchLocationsAddedUponMerger" xlink:label="NumberOfBranchLocationsAddedUponMerger" xlink:title="NumberOfBranchLocationsAddedUponMerger" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="NumberOfBranchLocationsAddedUponMerger" xlink:title="definition: BusinessAcquisitionLineItems to NumberOfBranchLocationsAddedUponMerger" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedTangibleAssetsNet" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedTangibleAssetsNet" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedTangibleAssetsNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedTangibleAssetsNet" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedTangibleAssetsNet" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_DecliningBalanceDepreciationMethodFactorOfStraightLineRateOfDepreciation" xlink:label="DecliningBalanceDepreciationMethodFactorOfStraightLineRateOfDepreciation" xlink:title="DecliningBalanceDepreciationMethodFactorOfStraightLineRateOfDepreciation" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="DecliningBalanceDepreciationMethodFactorOfStraightLineRateOfDepreciation" xlink:title="definition: BusinessAcquisitionLineItems to DecliningBalanceDepreciationMethodFactorOfStraightLineRateOfDepreciation" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1" xlink:label="FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1" xlink:title="FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1" xlink:title="definition: BusinessAcquisitionLineItems to FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_Revenues" xlink:label="Revenues" xlink:title="Revenues" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="Revenues" xlink:title="definition: BusinessAcquisitionLineItems to Revenues" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OperatingExpenses" xlink:label="OperatingExpenses" xlink:title="OperatingExpenses" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="OperatingExpenses" xlink:title="definition: BusinessAcquisitionLineItems to OperatingExpenses" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LiabilitiesFairValueAdjustment" xlink:label="LiabilitiesFairValueAdjustment" xlink:title="LiabilitiesFairValueAdjustment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="LiabilitiesFairValueAdjustment" xlink:title="definition: BusinessAcquisitionLineItems to LiabilitiesFairValueAdjustment" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_GoodwillPurchaseAccountingAdjustments" xlink:label="GoodwillPurchaseAccountingAdjustments" xlink:title="GoodwillPurchaseAccountingAdjustments" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="GoodwillPurchaseAccountingAdjustments" xlink:title="definition: BusinessAcquisitionLineItems to GoodwillPurchaseAccountingAdjustments" order="17.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="BusinessAcquisitionLineItems" xlink:to="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="definition: BusinessAcquisitionLineItems to ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="18.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_HRConsultantsSALLCMember" xlink:label="HRConsultantsSALLCMember" xlink:title="HRConsultantsSALLCMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="HRConsultantsSALLCMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to HRConsultantsSALLCMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_PennaAssociatesAgencyIncMember" xlink:label="PennaAssociatesAgencyIncMember" xlink:title="PennaAssociatesAgencyIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="PennaAssociatesAgencyIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to PennaAssociatesAgencyIncMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_StylesBridgesAssociatesMember" xlink:label="StylesBridgesAssociatesMember" xlink:title="StylesBridgesAssociatesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="StylesBridgesAssociatesMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to StylesBridgesAssociatesMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_GordonBRobertsAgencyIncMember" xlink:label="GordonBRobertsAgencyIncMember" xlink:title="GordonBRobertsAgencyIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="GordonBRobertsAgencyIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to GordonBRobertsAgencyIncMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_NortheastCapitalManagementIncMember" xlink:label="NortheastCapitalManagementIncMember" xlink:title="NortheastCapitalManagementIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="NortheastCapitalManagementIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to NortheastCapitalManagementIncMember" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_MerchantsBancsharesIncMember" xlink:label="MerchantsBancsharesIncMember" xlink:title="MerchantsBancsharesIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="MerchantsBancsharesIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to MerchantsBancsharesIncMember" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_DryfoosInsuranceAgencyIncMember" xlink:label="DryfoosInsuranceAgencyIncMember" xlink:title="DryfoosInsuranceAgencyIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="DryfoosInsuranceAgencyIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to DryfoosInsuranceAgencyIncMember" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_BenefitsAdvisoryServiceIncMember" xlink:label="BenefitsAdvisoryServiceIncMember" xlink:title="BenefitsAdvisoryServiceIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="BenefitsAdvisoryServiceIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to BenefitsAdvisoryServiceIncMember" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_NortheastRetirementServicesIncMember" xlink:label="NortheastRetirementServicesIncMember" xlink:title="NortheastRetirementServicesIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="NortheastRetirementServicesIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to NortheastRetirementServicesIncMember" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="FiniteLivedIntangibleAssetsByMajorClassAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to FiniteLivedIntangibleAssetsByMajorClassAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="FiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="definition: FiniteLivedIntangibleAssetsByMajorClassAxis to FiniteLivedIntangibleAssetsMajorClassNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="FiniteLivedIntangibleAssetsMajorClassNameDomain_2" xlink:title="FiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="FiniteLivedIntangibleAssetsMajorClassNameDomain_2" xlink:title="definition: FiniteLivedIntangibleAssetsByMajorClassAxis to FiniteLivedIntangibleAssetsMajorClassNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CustomerListsMember" xlink:label="CustomerListsMember" xlink:title="CustomerListsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="CustomerListsMember" xlink:title="definition: FiniteLivedIntangibleAssetsMajorClassNameDomain to CustomerListsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherIntangibleAssetsMember" xlink:label="OtherIntangibleAssetsMember" xlink:title="OtherIntangibleAssetsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="OtherIntangibleAssetsMember" xlink:title="definition: FiniteLivedIntangibleAssetsMajorClassNameDomain to OtherIntangibleAssetsMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_StatementGeographicalAxis" xlink:label="StatementGeographicalAxis" xlink:title="StatementGeographicalAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="StatementGeographicalAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to StatementGeographicalAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_SegmentGeographicalDomain" xlink:label="SegmentGeographicalDomain" xlink:title="SegmentGeographicalDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementGeographicalAxis" xlink:to="SegmentGeographicalDomain" xlink:title="definition: StatementGeographicalAxis to SegmentGeographicalDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_SegmentGeographicalDomain" xlink:label="SegmentGeographicalDomain_2" xlink:title="SegmentGeographicalDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementGeographicalAxis" xlink:to="SegmentGeographicalDomain_2" xlink:title="definition: StatementGeographicalAxis to SegmentGeographicalDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/stpr/2018/stpr-2018-01-31.xsd#stpr_VT" xlink:label="VT" xlink:title="VT" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentGeographicalDomain" xlink:to="VT" xlink:title="definition: SegmentGeographicalDomain to VT" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/stpr/2018/stpr-2018-01-31.xsd#stpr_MA" xlink:label="MA" xlink:title="MA" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentGeographicalDomain" xlink:to="MA" xlink:title="definition: SegmentGeographicalDomain to MA" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/AcquisitionsEstimatedFairValueOfAssetsAcquiredAndLiabilitiesAssumedDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="BusinessAcquisitionLineItems" xlink:title="BusinessAcquisitionLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferredIncludingEquityInterestInAcquireeHeldPriorToCombinationAbstract" xlink:label="BusinessCombinationConsiderationTransferredIncludingEquityInterestInAcquireeHeldPriorToCombinationAbstract" xlink:title="BusinessCombinationConsiderationTransferredIncludingEquityInterestInAcquireeHeldPriorToCombinationAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationConsiderationTransferredIncludingEquityInterestInAcquireeHeldPriorToCombinationAbstract" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationConsiderationTransferredIncludingEquityInterestInAcquireeHeldPriorToCombinationAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferredAbstract" xlink:label="BusinessCombinationConsiderationTransferredAbstract" xlink:title="BusinessCombinationConsiderationTransferredAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationConsiderationTransferredAbstract" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationConsiderationTransferredAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedLessNoncontrollingInterestAbstract" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedLessNoncontrollingInterestAbstract" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedLessNoncontrollingInterestAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedLessNoncontrollingInterestAbstract" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedLessNoncontrollingInterestAbstract" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_Goodwill" xlink:label="Goodwill" xlink:title="Goodwill" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="Goodwill" xlink:title="definition: BusinessAcquisitionLineItems to Goodwill" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoansAcquired" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoansAcquired" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoansAcquired" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoansAcquired" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoansAcquired" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDepositsAcquired" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDepositsAcquired" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDepositsAcquired" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDepositsAcquired" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDepositsAcquired" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedShortTermAdvances" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedShortTermAdvances" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedShortTermAdvances" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedShortTermAdvances" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedShortTermAdvances" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSecuritiesSoldUnderAgreementToRepurchaseShortTerm" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSecuritiesSoldUnderAgreementToRepurchaseShortTerm" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSecuritiesSoldUnderAgreementToRepurchaseShortTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSecuritiesSoldUnderAgreementToRepurchaseShortTerm" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSecuritiesSoldUnderAgreementToRepurchaseShortTerm" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSubordinatedDebtHeldByUnconsolidatedSubsidiaryTrusts" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSubordinatedDebtHeldByUnconsolidatedSubsidiaryTrusts" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSubordinatedDebtHeldByUnconsolidatedSubsidiaryTrusts" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSubordinatedDebtHeldByUnconsolidatedSubsidiaryTrusts" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSubordinatedDebtHeldByUnconsolidatedSubsidiaryTrusts" order="17.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet" xlink:label="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet" xlink:title="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet" order="18.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired" xlink:label="PaymentsToAcquireBusinessesNetOfCashAcquired" xlink:title="PaymentsToAcquireBusinessesNetOfCashAcquired" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="PaymentsToAcquireBusinessesNetOfCashAcquired" xlink:title="definition: BusinessAcquisitionLineItems to PaymentsToAcquireBusinessesNetOfCashAcquired" order="19.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:label="BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:title="BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" order="20.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferred1" xlink:label="BusinessCombinationConsiderationTransferred1" xlink:title="BusinessCombinationConsiderationTransferred1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="BusinessCombinationConsiderationTransferred1" xlink:title="definition: BusinessAcquisitionLineItems to BusinessCombinationConsiderationTransferred1" order="21.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="BusinessAcquisitionLineItems" xlink:to="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="definition: BusinessAcquisitionLineItems to ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="22.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_OtherAcquisitionsTwoMember" xlink:label="OtherAcquisitionsTwoMember" xlink:title="OtherAcquisitionsTwoMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OtherAcquisitionsTwoMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OtherAcquisitionsTwoMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_BenefitsAdvisoryServiceIncMember" xlink:label="BenefitsAdvisoryServiceIncMember" xlink:title="BenefitsAdvisoryServiceIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="BenefitsAdvisoryServiceIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to BenefitsAdvisoryServiceIncMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_NortheastRetirementServicesIncMember" xlink:label="NortheastRetirementServicesIncMember" xlink:title="NortheastRetirementServicesIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="NortheastRetirementServicesIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to NortheastRetirementServicesIncMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_MerchantsBancsharesIncMember" xlink:label="MerchantsBancsharesIncMember" xlink:title="MerchantsBancsharesIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="MerchantsBancsharesIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to MerchantsBancsharesIncMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_WJLAgenciesIncMember" xlink:label="WJLAgenciesIncMember" xlink:title="WJLAgenciesIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="WJLAgenciesIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to WJLAgenciesIncMember" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_OtherAcquisitionsMember" xlink:label="OtherAcquisitionsMember" xlink:title="OtherAcquisitionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="OtherAcquisitionsMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to OtherAcquisitionsMember" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_TotalAcquisitionsIn2017Member" xlink:label="TotalAcquisitionsIn2017Member" xlink:title="TotalAcquisitionsIn2017Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="TotalAcquisitionsIn2017Member" xlink:title="definition: BusinessAcquisitionAcquireeDomain to TotalAcquisitionsIn2017Member" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="FiniteLivedIntangibleAssetsByMajorClassAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to FiniteLivedIntangibleAssetsByMajorClassAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="FiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="definition: FiniteLivedIntangibleAssetsByMajorClassAxis to FiniteLivedIntangibleAssetsMajorClassNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="FiniteLivedIntangibleAssetsMajorClassNameDomain_2" xlink:title="FiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="FiniteLivedIntangibleAssetsMajorClassNameDomain_2" xlink:title="definition: FiniteLivedIntangibleAssetsByMajorClassAxis to FiniteLivedIntangibleAssetsMajorClassNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CoreDepositsMember" xlink:label="CoreDepositsMember" xlink:title="CoreDepositsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="CoreDepositsMember" xlink:title="definition: FiniteLivedIntangibleAssetsMajorClassNameDomain to CoreDepositsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherIntangibleAssetsMember" xlink:label="OtherIntangibleAssetsMember" xlink:title="OtherIntangibleAssetsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="OtherIntangibleAssetsMember" xlink:title="definition: FiniteLivedIntangibleAssetsMajorClassNameDomain to OtherIntangibleAssetsMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/AcquisitionsSummaryOfLoansAcquiredDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="BusinessAcquisitionLineItems" xlink:title="BusinessAcquisitionLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodAbstract" xlink:label="CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodAbstract" xlink:title="CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodAbstract" xlink:title="definition: BusinessAcquisitionLineItems to CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractuallyRequiredPaymentsReceivableAtAcquisition" xlink:label="CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractuallyRequiredPaymentsReceivableAtAcquisition" xlink:title="CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractuallyRequiredPaymentsReceivableAtAcquisition" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractuallyRequiredPaymentsReceivableAtAcquisition" xlink:title="definition: BusinessAcquisitionLineItems to CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractuallyRequiredPaymentsReceivableAtAcquisition" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractualCashFlowsNotExpectedToBeCollected" xlink:label="CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractualCashFlowsNotExpectedToBeCollected" xlink:title="CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractualCashFlowsNotExpectedToBeCollected" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractualCashFlowsNotExpectedToBeCollected" xlink:title="definition: BusinessAcquisitionLineItems to CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractualCashFlowsNotExpectedToBeCollected" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodCashFlowsExpectedToBeCollectedAtAcquisition" xlink:label="CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodCashFlowsExpectedToBeCollectedAtAcquisition" xlink:title="CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodCashFlowsExpectedToBeCollectedAtAcquisition" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodCashFlowsExpectedToBeCollectedAtAcquisition" xlink:title="definition: BusinessAcquisitionLineItems to CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodCashFlowsExpectedToBeCollectedAtAcquisition" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodInterestComponentOfCashFlows" xlink:label="CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodInterestComponentOfCashFlows" xlink:title="CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodInterestComponentOfCashFlows" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodInterestComponentOfCashFlows" xlink:title="definition: BusinessAcquisitionLineItems to CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodInterestComponentOfCashFlows" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodAtAcquisitionAtFairValue" xlink:label="CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodAtAcquisitionAtFairValue" xlink:title="CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodAtAcquisitionAtFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionLineItems" xlink:to="CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodAtAcquisitionAtFairValue" xlink:title="definition: BusinessAcquisitionLineItems to CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodAtAcquisitionAtFairValue" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="BusinessAcquisitionLineItems" xlink:to="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="definition: BusinessAcquisitionLineItems to ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="7.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_MerchantsBancsharesIncMember" xlink:label="MerchantsBancsharesIncMember" xlink:title="MerchantsBancsharesIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="MerchantsBancsharesIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to MerchantsBancsharesIncMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="FinancialInstrumentAxis" xlink:title="FinancialInstrumentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="FinancialInstrumentAxis" xlink:title="definition: ScheduleOfBusinessAcquisitionsByAcquisitionTable to FinancialInstrumentAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_AcquiredImpairedLoansMember" xlink:label="AcquiredImpairedLoansMember" xlink:title="AcquiredImpairedLoansMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="AcquiredImpairedLoansMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to AcquiredImpairedLoansMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_AcquiredNonImpairedLoansMember" xlink:label="AcquiredNonImpairedLoansMember" xlink:title="AcquiredNonImpairedLoansMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="AcquiredNonImpairedLoansMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to AcquiredNonImpairedLoansMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/AcquisitionsIntangibleAssetGoodwillAndAcquisitionrelatedExpensesDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="FiniteLivedIntangibleAssetsLineItems" xlink:title="FiniteLivedIntangibleAssetsLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:label="FiniteLivedIntangibleAssetsNetAbstract" xlink:title="FiniteLivedIntangibleAssetsNetAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FiniteLivedIntangibleAssetsLineItems" xlink:to="FiniteLivedIntangibleAssetsNetAbstract" xlink:title="definition: FiniteLivedIntangibleAssetsLineItems to FiniteLivedIntangibleAssetsNetAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="FiniteLivedIntangibleAssetUsefulLife" xlink:title="FiniteLivedIntangibleAssetUsefulLife" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FiniteLivedIntangibleAssetsLineItems" xlink:to="FiniteLivedIntangibleAssetUsefulLife" xlink:title="definition: FiniteLivedIntangibleAssetsLineItems to FiniteLivedIntangibleAssetUsefulLife" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:title="ScheduleOfFiniteLivedIntangibleAssetsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FiniteLivedIntangibleAssetsLineItems" xlink:to="ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:title="definition: FiniteLivedIntangibleAssetsLineItems to ScheduleOfFiniteLivedIntangibleAssetsTable" order="3.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:to="BusinessAcquisitionAxis" xlink:title="definition: ScheduleOfFiniteLivedIntangibleAssetsTable to BusinessAcquisitionAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_HRConsultantsSALLCMember" xlink:label="HRConsultantsSALLCMember" xlink:title="HRConsultantsSALLCMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="HRConsultantsSALLCMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to HRConsultantsSALLCMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_PennaAssociatesAgencyIncMember" xlink:label="PennaAssociatesAgencyIncMember" xlink:title="PennaAssociatesAgencyIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="PennaAssociatesAgencyIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to PennaAssociatesAgencyIncMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_StylesBridgesAssociatesMember" xlink:label="StylesBridgesAssociatesMember" xlink:title="StylesBridgesAssociatesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="StylesBridgesAssociatesMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to StylesBridgesAssociatesMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_GordonBRobertsAgencyIncMember" xlink:label="GordonBRobertsAgencyIncMember" xlink:title="GordonBRobertsAgencyIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="GordonBRobertsAgencyIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to GordonBRobertsAgencyIncMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_NortheastCapitalManagementIncMember" xlink:label="NortheastCapitalManagementIncMember" xlink:title="NortheastCapitalManagementIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="NortheastCapitalManagementIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to NortheastCapitalManagementIncMember" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_MerchantsBancsharesIncMember" xlink:label="MerchantsBancsharesIncMember" xlink:title="MerchantsBancsharesIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="MerchantsBancsharesIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to MerchantsBancsharesIncMember" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_DryfoosInsuranceAgencyIncMember" xlink:label="DryfoosInsuranceAgencyIncMember" xlink:title="DryfoosInsuranceAgencyIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="DryfoosInsuranceAgencyIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to DryfoosInsuranceAgencyIncMember" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_BenefitsAdvisoryServiceIncMember" xlink:label="BenefitsAdvisoryServiceIncMember" xlink:title="BenefitsAdvisoryServiceIncMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BusinessAcquisitionAcquireeDomain" xlink:to="BenefitsAdvisoryServiceIncMember" xlink:title="definition: BusinessAcquisitionAcquireeDomain to BenefitsAdvisoryServiceIncMember" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="FiniteLivedIntangibleAssetsByMajorClassAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:to="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="definition: ScheduleOfFiniteLivedIntangibleAssetsTable to FiniteLivedIntangibleAssetsByMajorClassAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="FiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="definition: FiniteLivedIntangibleAssetsByMajorClassAxis to FiniteLivedIntangibleAssetsMajorClassNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="FiniteLivedIntangibleAssetsMajorClassNameDomain_2" xlink:title="FiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="FiniteLivedIntangibleAssetsMajorClassNameDomain_2" xlink:title="definition: FiniteLivedIntangibleAssetsByMajorClassAxis to FiniteLivedIntangibleAssetsMajorClassNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CoreDepositsMember" xlink:label="CoreDepositsMember" xlink:title="CoreDepositsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="CoreDepositsMember" xlink:title="definition: FiniteLivedIntangibleAssetsMajorClassNameDomain to CoreDepositsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherIntangibleAssetsMember" xlink:label="OtherIntangibleAssetsMember" xlink:title="OtherIntangibleAssetsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="OtherIntangibleAssetsMember" xlink:title="definition: FiniteLivedIntangibleAssetsMajorClassNameDomain to OtherIntangibleAssetsMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/AccountingPoliciesDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:label="NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:title="NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesAbstract" xlink:label="NewAccountingPronouncementsAndChangesInAccountingPrinciplesAbstract" xlink:title="NewAccountingPronouncementsAndChangesInAccountingPrinciplesAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:to="NewAccountingPronouncementsAndChangesInAccountingPrinciplesAbstract" xlink:title="definition: NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems to NewAccountingPronouncementsAndChangesInAccountingPrinciplesAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubsequentEventsAbstract" xlink:label="SubsequentEventsAbstract" xlink:title="SubsequentEventsAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:to="SubsequentEventsAbstract" xlink:title="definition: NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems to SubsequentEventsAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_ProceedsFromRedemptionOfDebenturesAndPreferredSecurities" xlink:label="ProceedsFromRedemptionOfDebenturesAndPreferredSecurities" xlink:title="ProceedsFromRedemptionOfDebenturesAndPreferredSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:to="ProceedsFromRedemptionOfDebenturesAndPreferredSecurities" xlink:title="definition: NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems to ProceedsFromRedemptionOfDebenturesAndPreferredSecurities" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" xlink:label="CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" xlink:title="CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:to="CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" xlink:title="definition: NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems to CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LaborAndRelatedExpense" xlink:label="LaborAndRelatedExpense" xlink:title="LaborAndRelatedExpense" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:to="LaborAndRelatedExpense" xlink:title="definition: NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems to LaborAndRelatedExpense" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherNoninterestExpense" xlink:label="OtherNoninterestExpense" xlink:title="OtherNoninterestExpense" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:to="OtherNoninterestExpense" xlink:title="definition: NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems to OtherNoninterestExpense" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:label="NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:title="NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:to="NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:title="definition: NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems to NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" order="7.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="AdjustmentsForNewAccountingPronouncementsAxis" xlink:title="AdjustmentsForNewAccountingPronouncementsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="AdjustmentsForNewAccountingPronouncementsAxis" xlink:title="definition: NewAccountingPronouncementsOrChangeInAccountingPrincipleTable to AdjustmentsForNewAccountingPronouncementsAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="TypeOfAdoptionMember" xlink:title="TypeOfAdoptionMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="TypeOfAdoptionMember" xlink:title="definition: AdjustmentsForNewAccountingPronouncementsAxis to TypeOfAdoptionMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="TypeOfAdoptionMember_2" xlink:title="TypeOfAdoptionMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="TypeOfAdoptionMember_2" xlink:title="definition: AdjustmentsForNewAccountingPronouncementsAxis to TypeOfAdoptionMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccountingStandardsUpdate201707Member" xlink:label="AccountingStandardsUpdate201707Member" xlink:title="AccountingStandardsUpdate201707Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TypeOfAdoptionMember" xlink:to="AccountingStandardsUpdate201707Member" xlink:title="definition: TypeOfAdoptionMember to AccountingStandardsUpdate201707Member" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccountingStandardsUpdate201601Member" xlink:label="AccountingStandardsUpdate201601Member" xlink:title="AccountingStandardsUpdate201601Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TypeOfAdoptionMember" xlink:to="AccountingStandardsUpdate201601Member" xlink:title="definition: TypeOfAdoptionMember to AccountingStandardsUpdate201601Member" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="SubsequentEventTypeAxis" xlink:title="SubsequentEventTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="SubsequentEventTypeAxis" xlink:title="definition: NewAccountingPronouncementsOrChangeInAccountingPrincipleTable to SubsequentEventTypeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain_2" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain_2" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="SubsequentEventMember" xlink:title="SubsequentEventMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventTypeDomain" xlink:to="SubsequentEventMember" xlink:title="definition: SubsequentEventTypeDomain to SubsequentEventMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2018/dei-2018-01-31.xsd#dei_LegalEntityAxis" xlink:label="LegalEntityAxis" xlink:title="LegalEntityAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="LegalEntityAxis" xlink:title="definition: NewAccountingPronouncementsOrChangeInAccountingPrincipleTable to LegalEntityAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2018/dei-2018-01-31.xsd#dei_EntityDomain" xlink:label="EntityDomain" xlink:title="EntityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="LegalEntityAxis" xlink:to="EntityDomain" xlink:title="definition: LegalEntityAxis to EntityDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2018/dei-2018-01-31.xsd#dei_EntityDomain" xlink:label="EntityDomain_2" xlink:title="EntityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="LegalEntityAxis" xlink:to="EntityDomain_2" xlink:title="definition: LegalEntityAxis to EntityDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_CommunityStatutoryTrust3Member" xlink:label="CommunityStatutoryTrust3Member" xlink:title="CommunityStatutoryTrust3Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EntityDomain" xlink:to="CommunityStatutoryTrust3Member" xlink:title="definition: EntityDomain to CommunityStatutoryTrust3Member" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: NewAccountingPronouncementsOrChangeInAccountingPrincipleTable to StatementEquityComponentsAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_2" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="RetainedEarningsMember" xlink:title="RetainedEarningsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="RetainedEarningsMember" xlink:title="definition: EquityComponentDomain to RetainedEarningsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="AccumulatedOtherComprehensiveIncomeMember" xlink:title="AccumulatedOtherComprehensiveIncomeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="AccumulatedOtherComprehensiveIncomeMember" xlink:title="definition: EquityComponentDomain to AccumulatedOtherComprehensiveIncomeMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/InvestmentSecuritiesAvailableforsalePortfolioDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:label="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:title="ScheduleOfAvailableForSaleSecuritiesLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAbstract" xlink:label="AvailableForSaleSecuritiesAbstract" xlink:title="AvailableForSaleSecuritiesAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesAbstract" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesFairValueToAmortizedCostBasisAbstract" xlink:label="AvailableForSaleSecuritiesFairValueToAmortizedCostBasisAbstract" xlink:title="AvailableForSaleSecuritiesFairValueToAmortizedCostBasisAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesFairValueToAmortizedCostBasisAbstract" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesFairValueToAmortizedCostBasisAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_EquitySecuritiesAvailableForSaleFairValueToAmortizedCostBasisAbstract" xlink:label="EquitySecuritiesAvailableForSaleFairValueToAmortizedCostBasisAbstract" xlink:title="EquitySecuritiesAvailableForSaleFairValueToAmortizedCostBasisAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="EquitySecuritiesAvailableForSaleFairValueToAmortizedCostBasisAbstract" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to EquitySecuritiesAvailableForSaleFairValueToAmortizedCostBasisAbstract" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis" xlink:label="AvailableForSaleEquitySecuritiesAmortizedCostBasis" xlink:title="AvailableForSaleEquitySecuritiesAmortizedCostBasis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleEquitySecuritiesAmortizedCostBasis" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleEquitySecuritiesAmortizedCostBasis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:label="AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:title="AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:label="AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:title="AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesEquitySecurities" xlink:label="AvailableForSaleSecuritiesEquitySecurities" xlink:title="AvailableForSaleSecuritiesEquitySecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesEquitySecurities" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesEquitySecurities" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:label="AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:title="AvailableForSaleDebtSecuritiesAmortizedCostBasis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleDebtSecuritiesAmortizedCostBasis" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:label="AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:title="AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:label="AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:title="AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="AvailableForSaleSecuritiesDebtSecurities" xlink:title="AvailableForSaleSecuritiesDebtSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtSecurities" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtSecurities" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAmortizedCost" xlink:label="AvailableForSaleSecuritiesAmortizedCost" xlink:title="AvailableForSaleSecuritiesAmortizedCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesAmortizedCost" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesAmortizedCost" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:label="AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:title="AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:label="AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:title="AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecurities" xlink:label="AvailableForSaleSecurities" xlink:title="AvailableForSaleSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecurities" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecurities" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:label="ScheduleOfAvailableForSaleSecuritiesTable" xlink:title="ScheduleOfAvailableForSaleSecuritiesTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="ScheduleOfAvailableForSaleSecuritiesTable" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to ScheduleOfAvailableForSaleSecuritiesTable" order="16.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="FinancialInstrumentAxis" xlink:title="FinancialInstrumentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfAvailableForSaleSecuritiesTable" xlink:to="FinancialInstrumentAxis" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesTable to FinancialInstrumentAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_USTreasuryAndGovernmentMember" xlink:label="USTreasuryAndGovernmentMember" xlink:title="USTreasuryAndGovernmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="USTreasuryAndGovernmentMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to USTreasuryAndGovernmentMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember" xlink:label="USStatesAndPoliticalSubdivisionsMember" xlink:title="USStatesAndPoliticalSubdivisionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="USStatesAndPoliticalSubdivisionsMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to USStatesAndPoliticalSubdivisionsMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:label="MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:title="MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="CorporateDebtSecuritiesMember" xlink:title="CorporateDebtSecuritiesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="CorporateDebtSecuritiesMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to CorporateDebtSecuritiesMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_GovernmentAgencyCollateralizedMortgageObligationsMember" xlink:label="GovernmentAgencyCollateralizedMortgageObligationsMember" xlink:title="GovernmentAgencyCollateralizedMortgageObligationsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="GovernmentAgencyCollateralizedMortgageObligationsMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to GovernmentAgencyCollateralizedMortgageObligationsMember" order="5.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/InvestmentSecuritiesEquityAndOtherSecuritiesDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:label="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:title="ScheduleOfAvailableForSaleSecuritiesLineItems" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_EquityAndOtherSecuritiesAbstract" xlink:label="EquityAndOtherSecuritiesAbstract" xlink:title="EquityAndOtherSecuritiesAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="EquityAndOtherSecuritiesAbstract" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to EquityAndOtherSecuritiesAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_EquitySecuritiesFVNIAbstract" xlink:label="EquitySecuritiesFVNIAbstract" xlink:title="EquitySecuritiesFVNIAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="EquitySecuritiesFVNIAbstract" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to EquitySecuritiesFVNIAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_OtherSecuritiesAbstract" xlink:label="OtherSecuritiesAbstract" xlink:title="OtherSecuritiesAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="OtherSecuritiesAbstract" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to OtherSecuritiesAbstract" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherInvestmentsAndSecuritiesAtCost" xlink:label="OtherInvestmentsAndSecuritiesAtCost" xlink:title="OtherInvestmentsAndSecuritiesAtCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="OtherInvestmentsAndSecuritiesAtCost" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to OtherInvestmentsAndSecuritiesAtCost" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_OtherInvestmentsAndSecuritiesFairValue" xlink:label="OtherInvestmentsAndSecuritiesFairValue" xlink:title="OtherInvestmentsAndSecuritiesFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="OtherInvestmentsAndSecuritiesFairValue" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to OtherInvestmentsAndSecuritiesFairValue" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EquitySecuritiesFvNiCost" xlink:label="EquitySecuritiesFvNiCost" xlink:title="EquitySecuritiesFvNiCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="EquitySecuritiesFvNiCost" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to EquitySecuritiesFvNiCost" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_EquitySecuritiesFVNIAccumulatedGrossUnrealizedGainBeforeTax" xlink:label="EquitySecuritiesFVNIAccumulatedGrossUnrealizedGainBeforeTax" xlink:title="EquitySecuritiesFVNIAccumulatedGrossUnrealizedGainBeforeTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="EquitySecuritiesFVNIAccumulatedGrossUnrealizedGainBeforeTax" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to EquitySecuritiesFVNIAccumulatedGrossUnrealizedGainBeforeTax" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_EquitySecuritiesFVNIAccumulatedGrossUnrealizedLossBeforeTax" xlink:label="EquitySecuritiesFVNIAccumulatedGrossUnrealizedLossBeforeTax" xlink:title="EquitySecuritiesFVNIAccumulatedGrossUnrealizedLossBeforeTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="EquitySecuritiesFVNIAccumulatedGrossUnrealizedLossBeforeTax" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to EquitySecuritiesFVNIAccumulatedGrossUnrealizedLossBeforeTax" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EquitySecuritiesFvNi" xlink:label="EquitySecuritiesFvNi" xlink:title="EquitySecuritiesFvNi" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="EquitySecuritiesFvNi" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to EquitySecuritiesFvNi" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_OtherInvestmentsAndEquitySecuritiesAtCost" xlink:label="OtherInvestmentsAndEquitySecuritiesAtCost" xlink:title="OtherInvestmentsAndEquitySecuritiesAtCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="OtherInvestmentsAndEquitySecuritiesAtCost" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to OtherInvestmentsAndEquitySecuritiesAtCost" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:label="OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:title="OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:label="OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:title="OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_OtherInvestmentAndEquitySecuritiesFairValue" xlink:label="OtherInvestmentAndEquitySecuritiesFairValue" xlink:title="OtherInvestmentAndEquitySecuritiesFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="OtherInvestmentAndEquitySecuritiesFairValue" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to OtherInvestmentAndEquitySecuritiesFairValue" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:label="ScheduleOfAvailableForSaleSecuritiesTable" xlink:title="ScheduleOfAvailableForSaleSecuritiesTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="ScheduleOfAvailableForSaleSecuritiesTable" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to ScheduleOfAvailableForSaleSecuritiesTable" order="14.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="FinancialInstrumentAxis" xlink:title="FinancialInstrumentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfAvailableForSaleSecuritiesTable" xlink:to="FinancialInstrumentAxis" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesTable to FinancialInstrumentAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_InvestmentInFederalHomeLoanBankStockMember" xlink:label="InvestmentInFederalHomeLoanBankStockMember" xlink:title="InvestmentInFederalHomeLoanBankStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="InvestmentInFederalHomeLoanBankStockMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to InvestmentInFederalHomeLoanBankStockMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_FederalReserveBankStockMember" xlink:label="FederalReserveBankStockMember" xlink:title="FederalReserveBankStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="FederalReserveBankStockMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to FederalReserveBankStockMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CertificatesOfDepositMember" xlink:label="CertificatesOfDepositMember" xlink:title="CertificatesOfDepositMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="CertificatesOfDepositMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to CertificatesOfDepositMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_OtherEquitySecuritiesMember" xlink:label="OtherEquitySecuritiesMember" xlink:title="OtherEquitySecuritiesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="OtherEquitySecuritiesMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to OtherEquitySecuritiesMember" order="4.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/InvestmentSecuritiesInvestmentSecuritiesInContinuousUnrealizedLossPositionDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:label="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:title="ScheduleOfAvailableForSaleSecuritiesLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsAbstract" xlink:label="AvailableForsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsAbstract" xlink:title="AvailableForsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsAbstract" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" xlink:label="AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" xlink:title="AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:label="AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:title="AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" xlink:label="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" xlink:title="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" xlink:label="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" xlink:title="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:label="DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:title="DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months" xlink:label="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months" xlink:title="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger" xlink:label="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger" xlink:title="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:label="DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:title="DebtSecuritiesAvailableForSaleUnrealizedLossPosition" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to DebtSecuritiesAvailableForSaleUnrealizedLossPosition" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions" xlink:label="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions" xlink:title="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions" xlink:label="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions" xlink:title="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions" xlink:label="DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions" xlink:title="DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:label="ScheduleOfAvailableForSaleSecuritiesTable" xlink:title="ScheduleOfAvailableForSaleSecuritiesTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="ScheduleOfAvailableForSaleSecuritiesTable" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to ScheduleOfAvailableForSaleSecuritiesTable" order="13.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="FinancialInstrumentAxis" xlink:title="FinancialInstrumentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfAvailableForSaleSecuritiesTable" xlink:to="FinancialInstrumentAxis" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesTable to FinancialInstrumentAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_USTreasuryAndGovernmentMember" xlink:label="USTreasuryAndGovernmentMember" xlink:title="USTreasuryAndGovernmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="USTreasuryAndGovernmentMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to USTreasuryAndGovernmentMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember" xlink:label="USStatesAndPoliticalSubdivisionsMember" xlink:title="USStatesAndPoliticalSubdivisionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="USStatesAndPoliticalSubdivisionsMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to USStatesAndPoliticalSubdivisionsMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:label="MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:title="MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="CorporateDebtSecuritiesMember" xlink:title="CorporateDebtSecuritiesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="CorporateDebtSecuritiesMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to CorporateDebtSecuritiesMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_GovernmentAgencyCollateralizedMortgageObligationsMember" xlink:label="GovernmentAgencyCollateralizedMortgageObligationsMember" xlink:title="GovernmentAgencyCollateralizedMortgageObligationsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="GovernmentAgencyCollateralizedMortgageObligationsMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to GovernmentAgencyCollateralizedMortgageObligationsMember" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_MarketableEquitySecurityMember" xlink:label="MarketableEquitySecurityMember" xlink:title="MarketableEquitySecurityMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="MarketableEquitySecurityMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to MarketableEquitySecurityMember" order="6.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/InvestmentSecuritiesAmortizedCostAndEstimatedFairValueOfDebtSecuritiesByContractualMaturityDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:label="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:title="ScheduleOfAvailableForSaleSecuritiesLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract" xlink:label="AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAbstract" xlink:label="AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAbstract" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAbstract" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged" xlink:label="PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged" xlink:title="PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" xlink:label="AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue" xlink:label="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue" xlink:label="AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue" xlink:label="AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate" xlink:label="AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" xlink:label="AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="AvailableForSaleSecuritiesDebtSecurities" xlink:title="AvailableForSaleSecuritiesDebtSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtSecurities" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtSecurities" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost" xlink:label="AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost" xlink:label="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost" xlink:label="AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost" xlink:label="AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost" order="14.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis" xlink:label="AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost" xlink:label="AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:label="AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:title="AvailableForSaleDebtSecuritiesAmortizedCostBasis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to AvailableForSaleDebtSecuritiesAmortizedCostBasis" order="17.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:label="ScheduleOfAvailableForSaleSecuritiesTable" xlink:title="ScheduleOfAvailableForSaleSecuritiesTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="ScheduleOfAvailableForSaleSecuritiesTable" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesLineItems to ScheduleOfAvailableForSaleSecuritiesTable" order="18.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="FinancialInstrumentAxis" xlink:title="FinancialInstrumentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfAvailableForSaleSecuritiesTable" xlink:to="FinancialInstrumentAxis" xlink:title="definition: ScheduleOfAvailableForSaleSecuritiesTable to FinancialInstrumentAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:label="MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:title="MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_GovernmentAgencyCollateralizedMortgageObligationsMember" xlink:label="GovernmentAgencyCollateralizedMortgageObligationsMember" xlink:title="GovernmentAgencyCollateralizedMortgageObligationsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="GovernmentAgencyCollateralizedMortgageObligationsMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to GovernmentAgencyCollateralizedMortgageObligationsMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_USTreasuryAndGovernmentMember" xlink:label="USTreasuryAndGovernmentMember" xlink:title="USTreasuryAndGovernmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="USTreasuryAndGovernmentMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to USTreasuryAndGovernmentMember" order="3.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/LoansLoanSummaryDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LoansAndLeasesReceivableDisclosureLineItems" xlink:label="LoansAndLeasesReceivableDisclosureLineItems" xlink:title="LoansAndLeasesReceivableDisclosureLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NotesReceivableNetAbstract" xlink:label="NotesReceivableNetAbstract" xlink:title="NotesReceivableNetAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LoansAndLeasesReceivableDisclosureLineItems" xlink:to="NotesReceivableNetAbstract" xlink:title="definition: LoansAndLeasesReceivableDisclosureLineItems to NotesReceivableNetAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_FinancialReceivableContractTerm" xlink:label="FinancialReceivableContractTerm" xlink:title="FinancialReceivableContractTerm" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LoansAndLeasesReceivableDisclosureLineItems" xlink:to="FinancialReceivableContractTerm" xlink:title="definition: LoansAndLeasesReceivableDisclosureLineItems to FinancialReceivableContractTerm" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LoansAndLeasesReceivableGrossCarryingAmount" xlink:label="LoansAndLeasesReceivableGrossCarryingAmount" xlink:title="LoansAndLeasesReceivableGrossCarryingAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LoansAndLeasesReceivableDisclosureLineItems" xlink:to="LoansAndLeasesReceivableGrossCarryingAmount" xlink:title="definition: LoansAndLeasesReceivableDisclosureLineItems to LoansAndLeasesReceivableGrossCarryingAmount" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LoansAndLeasesReceivableAllowance" xlink:label="LoansAndLeasesReceivableAllowance" xlink:title="LoansAndLeasesReceivableAllowance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LoansAndLeasesReceivableDisclosureLineItems" xlink:to="LoansAndLeasesReceivableAllowance" xlink:title="definition: LoansAndLeasesReceivableDisclosureLineItems to LoansAndLeasesReceivableAllowance" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetReportedAmount" xlink:label="LoansAndLeasesReceivableNetReportedAmount" xlink:title="LoansAndLeasesReceivableNetReportedAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LoansAndLeasesReceivableDisclosureLineItems" xlink:to="LoansAndLeasesReceivableNetReportedAmount" xlink:title="definition: LoansAndLeasesReceivableDisclosureLineItems to LoansAndLeasesReceivableNetReportedAmount" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LoansAndLeasesReceivableDisclosureTable" xlink:label="LoansAndLeasesReceivableDisclosureTable" xlink:title="LoansAndLeasesReceivableDisclosureTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="LoansAndLeasesReceivableDisclosureLineItems" xlink:to="LoansAndLeasesReceivableDisclosureTable" xlink:title="definition: LoansAndLeasesReceivableDisclosureLineItems to LoansAndLeasesReceivableDisclosureTable" order="6.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="FinancingReceivablePortfolioSegmentAxis" xlink:title="FinancingReceivablePortfolioSegmentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="LoansAndLeasesReceivableDisclosureTable" xlink:to="FinancingReceivablePortfolioSegmentAxis" xlink:title="definition: LoansAndLeasesReceivableDisclosureTable to FinancingReceivablePortfolioSegmentAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="FinancingReceivablePortfolioSegmentDomain" xlink:title="FinancingReceivablePortfolioSegmentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancingReceivablePortfolioSegmentAxis" xlink:to="FinancingReceivablePortfolioSegmentDomain" xlink:title="definition: FinancingReceivablePortfolioSegmentAxis to FinancingReceivablePortfolioSegmentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="FinancingReceivablePortfolioSegmentDomain_2" xlink:title="FinancingReceivablePortfolioSegmentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancingReceivablePortfolioSegmentAxis" xlink:to="FinancingReceivablePortfolioSegmentDomain_2" xlink:title="definition: FinancingReceivablePortfolioSegmentAxis to FinancingReceivablePortfolioSegmentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="CommercialPortfolioSegmentMember" xlink:title="CommercialPortfolioSegmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivablePortfolioSegmentDomain" xlink:to="CommercialPortfolioSegmentMember" xlink:title="definition: FinancingReceivablePortfolioSegmentDomain to CommercialPortfolioSegmentMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ResidentialPortfolioSegmentMember" xlink:label="ResidentialPortfolioSegmentMember" xlink:title="ResidentialPortfolioSegmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivablePortfolioSegmentDomain" xlink:to="ResidentialPortfolioSegmentMember" xlink:title="definition: FinancingReceivablePortfolioSegmentDomain to ResidentialPortfolioSegmentMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:label="ConsumerPortfolioSegmentMember" xlink:title="ConsumerPortfolioSegmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivablePortfolioSegmentDomain" xlink:to="ConsumerPortfolioSegmentMember" xlink:title="definition: FinancingReceivablePortfolioSegmentDomain to ConsumerPortfolioSegmentMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:title="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="LoansAndLeasesReceivableDisclosureTable" xlink:to="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:title="definition: LoansAndLeasesReceivableDisclosureTable to FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:title="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:title="definition: FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis to FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" xlink:title="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" xlink:title="definition: FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis to FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommercialLoanMember" xlink:label="CommercialLoanMember" xlink:title="CommercialLoanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="CommercialLoanMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to CommercialLoanMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ResidentialMortgageMember" xlink:label="ResidentialMortgageMember" xlink:title="ResidentialMortgageMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="ResidentialMortgageMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to ResidentialMortgageMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_ConsumerInstallmentIndirectMember" xlink:label="ConsumerInstallmentIndirectMember" xlink:title="ConsumerInstallmentIndirectMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="ConsumerInstallmentIndirectMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to ConsumerInstallmentIndirectMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_ConsumerInstallmentDirectMember" xlink:label="ConsumerInstallmentDirectMember" xlink:title="ConsumerInstallmentDirectMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="ConsumerInstallmentDirectMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to ConsumerInstallmentDirectMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_HomeEquityReceivablesMember" xlink:label="HomeEquityReceivablesMember" xlink:title="HomeEquityReceivablesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="HomeEquityReceivablesMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to HomeEquityReceivablesMember" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="LoansAndLeasesReceivableDisclosureTable" xlink:to="RangeAxis" xlink:title="definition: LoansAndLeasesReceivableDisclosureTable to RangeAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeMember" xlink:label="RangeMember_2" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember_2" xlink:title="definition: RangeAxis to RangeMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_MinimumMember" xlink:label="MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MinimumMember" xlink:title="definition: RangeMember to MinimumMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_MaximumMember" xlink:label="MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MaximumMember" xlink:title="definition: RangeMember to MaximumMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/LoansCreditQualityByPastDueStatusDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:label="FinancingReceivableRecordedInvestmentLineItems" xlink:title="FinancingReceivableRecordedInvestmentLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentAgingAbstract" xlink:label="FinancingReceivableRecordedInvestmentAgingAbstract" xlink:title="FinancingReceivableRecordedInvestmentAgingAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentLineItems" xlink:to="FinancingReceivableRecordedInvestmentAgingAbstract" xlink:title="definition: FinancingReceivableRecordedInvestmentLineItems to FinancingReceivableRecordedInvestmentAgingAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" xlink:label="FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" xlink:title="FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentLineItems" xlink:to="FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" xlink:title="definition: FinancingReceivableRecordedInvestmentLineItems to FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus" xlink:label="FinancingReceivableRecordedInvestmentNonaccrualStatus" xlink:title="FinancingReceivableRecordedInvestmentNonaccrualStatus" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentLineItems" xlink:to="FinancingReceivableRecordedInvestmentNonaccrualStatus" xlink:title="definition: FinancingReceivableRecordedInvestmentLineItems to FinancingReceivableRecordedInvestmentNonaccrualStatus" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDue" xlink:label="FinancingReceivableRecordedInvestmentPastDue" xlink:title="FinancingReceivableRecordedInvestmentPastDue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentLineItems" xlink:to="FinancingReceivableRecordedInvestmentPastDue" xlink:title="definition: FinancingReceivableRecordedInvestmentLineItems to FinancingReceivableRecordedInvestmentPastDue" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_FinancingReceivableRecordedInvestmentPurchasedImpaired" xlink:label="FinancingReceivableRecordedInvestmentPurchasedImpaired" xlink:title="FinancingReceivableRecordedInvestmentPurchasedImpaired" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentLineItems" xlink:to="FinancingReceivableRecordedInvestmentPurchasedImpaired" xlink:title="definition: FinancingReceivableRecordedInvestmentLineItems to FinancingReceivableRecordedInvestmentPurchasedImpaired" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentCurrent" xlink:label="FinancingReceivableRecordedInvestmentCurrent" xlink:title="FinancingReceivableRecordedInvestmentCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentLineItems" xlink:to="FinancingReceivableRecordedInvestmentCurrent" xlink:title="definition: FinancingReceivableRecordedInvestmentLineItems to FinancingReceivableRecordedInvestmentCurrent" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LoansAndLeasesReceivableGrossCarryingAmount" xlink:label="LoansAndLeasesReceivableGrossCarryingAmount" xlink:title="LoansAndLeasesReceivableGrossCarryingAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentLineItems" xlink:to="LoansAndLeasesReceivableGrossCarryingAmount" xlink:title="definition: FinancingReceivableRecordedInvestmentLineItems to LoansAndLeasesReceivableGrossCarryingAmount" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable" xlink:label="ScheduleOfFinancingReceivablesPastDueTable" xlink:title="ScheduleOfFinancingReceivablesPastDueTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FinancingReceivableRecordedInvestmentLineItems" xlink:to="ScheduleOfFinancingReceivablesPastDueTable" xlink:title="definition: FinancingReceivableRecordedInvestmentLineItems to ScheduleOfFinancingReceivablesPastDueTable" order="8.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="FinancingReceivablePortfolioSegmentAxis" xlink:title="FinancingReceivablePortfolioSegmentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFinancingReceivablesPastDueTable" xlink:to="FinancingReceivablePortfolioSegmentAxis" xlink:title="definition: ScheduleOfFinancingReceivablesPastDueTable to FinancingReceivablePortfolioSegmentAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="FinancingReceivablePortfolioSegmentDomain" xlink:title="FinancingReceivablePortfolioSegmentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancingReceivablePortfolioSegmentAxis" xlink:to="FinancingReceivablePortfolioSegmentDomain" xlink:title="definition: FinancingReceivablePortfolioSegmentAxis to FinancingReceivablePortfolioSegmentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="FinancingReceivablePortfolioSegmentDomain_2" xlink:title="FinancingReceivablePortfolioSegmentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancingReceivablePortfolioSegmentAxis" xlink:to="FinancingReceivablePortfolioSegmentDomain_2" xlink:title="definition: FinancingReceivablePortfolioSegmentAxis to FinancingReceivablePortfolioSegmentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="CommercialPortfolioSegmentMember" xlink:title="CommercialPortfolioSegmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivablePortfolioSegmentDomain" xlink:to="CommercialPortfolioSegmentMember" xlink:title="definition: FinancingReceivablePortfolioSegmentDomain to CommercialPortfolioSegmentMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ResidentialPortfolioSegmentMember" xlink:label="ResidentialPortfolioSegmentMember" xlink:title="ResidentialPortfolioSegmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivablePortfolioSegmentDomain" xlink:to="ResidentialPortfolioSegmentMember" xlink:title="definition: FinancingReceivablePortfolioSegmentDomain to ResidentialPortfolioSegmentMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:label="ConsumerPortfolioSegmentMember" xlink:title="ConsumerPortfolioSegmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivablePortfolioSegmentDomain" xlink:to="ConsumerPortfolioSegmentMember" xlink:title="definition: FinancingReceivablePortfolioSegmentDomain to ConsumerPortfolioSegmentMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:title="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFinancingReceivablesPastDueTable" xlink:to="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:title="definition: ScheduleOfFinancingReceivablesPastDueTable to FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:title="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:title="definition: FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis to FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" xlink:title="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" xlink:title="definition: FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis to FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommercialLoanMember" xlink:label="CommercialLoanMember" xlink:title="CommercialLoanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="CommercialLoanMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to CommercialLoanMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ResidentialMortgageMember" xlink:label="ResidentialMortgageMember" xlink:title="ResidentialMortgageMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="ResidentialMortgageMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to ResidentialMortgageMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_ConsumerInstallmentIndirectMember" xlink:label="ConsumerInstallmentIndirectMember" xlink:title="ConsumerInstallmentIndirectMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="ConsumerInstallmentIndirectMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to ConsumerInstallmentIndirectMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_ConsumerInstallmentDirectMember" xlink:label="ConsumerInstallmentDirectMember" xlink:title="ConsumerInstallmentDirectMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="ConsumerInstallmentDirectMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to ConsumerInstallmentDirectMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_HomeEquityReceivablesMember" xlink:label="HomeEquityReceivablesMember" xlink:title="HomeEquityReceivablesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="HomeEquityReceivablesMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to HomeEquityReceivablesMember" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:label="AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:title="AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFinancingReceivablesPastDueTable" xlink:to="AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:title="definition: ScheduleOfFinancingReceivablesPastDueTable to AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ReceivableTypeDomain" xlink:label="ReceivableTypeDomain" xlink:title="ReceivableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="ReceivableTypeDomain" xlink:title="definition: AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis to ReceivableTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ReceivableTypeDomain" xlink:label="ReceivableTypeDomain_2" xlink:title="ReceivableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="ReceivableTypeDomain_2" xlink:title="definition: AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis to ReceivableTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_LegacyLoanMember" xlink:label="LegacyLoanMember" xlink:title="LegacyLoanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ReceivableTypeDomain" xlink:to="LegacyLoanMember" xlink:title="definition: ReceivableTypeDomain to LegacyLoanMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_AcquiredLoansMember" xlink:label="AcquiredLoansMember" xlink:title="AcquiredLoansMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ReceivableTypeDomain" xlink:to="AcquiredLoansMember" xlink:title="definition: ReceivableTypeDomain to AcquiredLoansMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:label="FinancingReceivablesPeriodPastDueAxis" xlink:title="FinancingReceivablesPeriodPastDueAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFinancingReceivablesPastDueTable" xlink:to="FinancingReceivablesPeriodPastDueAxis" xlink:title="definition: ScheduleOfFinancingReceivablesPastDueTable to FinancingReceivablesPeriodPastDueAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:label="FinancingReceivablesPeriodPastDueDomain" xlink:title="FinancingReceivablesPeriodPastDueDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancingReceivablesPeriodPastDueAxis" xlink:to="FinancingReceivablesPeriodPastDueDomain" xlink:title="definition: FinancingReceivablesPeriodPastDueAxis to FinancingReceivablesPeriodPastDueDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:label="FinancingReceivablesPeriodPastDueDomain_2" xlink:title="FinancingReceivablesPeriodPastDueDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancingReceivablesPeriodPastDueAxis" xlink:to="FinancingReceivablesPeriodPastDueDomain_2" xlink:title="definition: FinancingReceivablesPeriodPastDueAxis to FinancingReceivablesPeriodPastDueDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_FinancingReceivables30To89DaysPastDueMember" xlink:label="FinancingReceivables30To89DaysPastDueMember" xlink:title="FinancingReceivables30To89DaysPastDueMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivablesPeriodPastDueDomain" xlink:to="FinancingReceivables30To89DaysPastDueMember" xlink:title="definition: FinancingReceivablesPeriodPastDueDomain to FinancingReceivables30To89DaysPastDueMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/LoansAmountOfBusinessLendingLoansByCreditQualityCategoryDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:label="FinancingReceivableRecordedInvestmentLineItems" xlink:title="FinancingReceivableRecordedInvestmentLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LoansAndLeasesReceivableBeforeFeesGrossAbstract" xlink:label="LoansAndLeasesReceivableBeforeFeesGrossAbstract" xlink:title="LoansAndLeasesReceivableBeforeFeesGrossAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentLineItems" xlink:to="LoansAndLeasesReceivableBeforeFeesGrossAbstract" xlink:title="definition: FinancingReceivableRecordedInvestmentLineItems to LoansAndLeasesReceivableBeforeFeesGrossAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LoansAndLeasesReceivableGrossCarryingAmount" xlink:label="LoansAndLeasesReceivableGrossCarryingAmount" xlink:title="LoansAndLeasesReceivableGrossCarryingAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentLineItems" xlink:to="LoansAndLeasesReceivableGrossCarryingAmount" xlink:title="definition: FinancingReceivableRecordedInvestmentLineItems to LoansAndLeasesReceivableGrossCarryingAmount" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:label="ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:title="ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FinancingReceivableRecordedInvestmentLineItems" xlink:to="ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:title="definition: FinancingReceivableRecordedInvestmentLineItems to ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" order="3.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:title="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:title="definition: ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable to FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:title="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:title="definition: FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis to FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" xlink:title="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" xlink:title="definition: FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis to FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommercialLoanMember" xlink:label="CommercialLoanMember" xlink:title="CommercialLoanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="CommercialLoanMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to CommercialLoanMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_AllOtherLoansMember" xlink:label="AllOtherLoansMember" xlink:title="AllOtherLoansMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="AllOtherLoansMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to AllOtherLoansMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ResidentialMortgageMember" xlink:label="ResidentialMortgageMember" xlink:title="ResidentialMortgageMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllOtherLoansMember" xlink:to="ResidentialMortgageMember" xlink:title="definition: AllOtherLoansMember to ResidentialMortgageMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_ConsumerInstallmentIndirectMember" xlink:label="ConsumerInstallmentIndirectMember" xlink:title="ConsumerInstallmentIndirectMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllOtherLoansMember" xlink:to="ConsumerInstallmentIndirectMember" xlink:title="definition: AllOtherLoansMember to ConsumerInstallmentIndirectMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_ConsumerInstallmentDirectMember" xlink:label="ConsumerInstallmentDirectMember" xlink:title="ConsumerInstallmentDirectMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllOtherLoansMember" xlink:to="ConsumerInstallmentDirectMember" xlink:title="definition: AllOtherLoansMember to ConsumerInstallmentDirectMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_HomeEquityReceivablesMember" xlink:label="HomeEquityReceivablesMember" xlink:title="HomeEquityReceivablesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllOtherLoansMember" xlink:to="HomeEquityReceivablesMember" xlink:title="definition: AllOtherLoansMember to HomeEquityReceivablesMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_InternalCreditAssessmentAxis" xlink:label="InternalCreditAssessmentAxis" xlink:title="InternalCreditAssessmentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="InternalCreditAssessmentAxis" xlink:title="definition: ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable to InternalCreditAssessmentAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_InternalCreditAssessmentDomain" xlink:label="InternalCreditAssessmentDomain" xlink:title="InternalCreditAssessmentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="InternalCreditAssessmentAxis" xlink:to="InternalCreditAssessmentDomain" xlink:title="definition: InternalCreditAssessmentAxis to InternalCreditAssessmentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_InternalCreditAssessmentDomain" xlink:label="InternalCreditAssessmentDomain_2" xlink:title="InternalCreditAssessmentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="InternalCreditAssessmentAxis" xlink:to="InternalCreditAssessmentDomain_2" xlink:title="definition: InternalCreditAssessmentAxis to InternalCreditAssessmentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PassMember" xlink:label="PassMember" xlink:title="PassMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="InternalCreditAssessmentDomain" xlink:to="PassMember" xlink:title="definition: InternalCreditAssessmentDomain to PassMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SpecialMentionMember" xlink:label="SpecialMentionMember" xlink:title="SpecialMentionMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="InternalCreditAssessmentDomain" xlink:to="SpecialMentionMember" xlink:title="definition: InternalCreditAssessmentDomain to SpecialMentionMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubstandardMember" xlink:label="SubstandardMember" xlink:title="SubstandardMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="InternalCreditAssessmentDomain" xlink:to="SubstandardMember" xlink:title="definition: InternalCreditAssessmentDomain to SubstandardMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DoubtfulMember" xlink:label="DoubtfulMember" xlink:title="DoubtfulMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="InternalCreditAssessmentDomain" xlink:to="DoubtfulMember" xlink:title="definition: InternalCreditAssessmentDomain to DoubtfulMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_PurchasedImpairedMember" xlink:label="PurchasedImpairedMember" xlink:title="PurchasedImpairedMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="InternalCreditAssessmentDomain" xlink:to="PurchasedImpairedMember" xlink:title="definition: InternalCreditAssessmentDomain to PurchasedImpairedMember" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancialInstrumentPerformanceStatusAxis" xlink:label="FinancialInstrumentPerformanceStatusAxis" xlink:title="FinancialInstrumentPerformanceStatusAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="FinancialInstrumentPerformanceStatusAxis" xlink:title="definition: ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable to FinancialInstrumentPerformanceStatusAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancialInstrumentPerformanceStatusDomain" xlink:label="FinancialInstrumentPerformanceStatusDomain" xlink:title="FinancialInstrumentPerformanceStatusDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancialInstrumentPerformanceStatusAxis" xlink:to="FinancialInstrumentPerformanceStatusDomain" xlink:title="definition: FinancialInstrumentPerformanceStatusAxis to FinancialInstrumentPerformanceStatusDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancialInstrumentPerformanceStatusDomain" xlink:label="FinancialInstrumentPerformanceStatusDomain_2" xlink:title="FinancialInstrumentPerformanceStatusDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancialInstrumentPerformanceStatusAxis" xlink:to="FinancialInstrumentPerformanceStatusDomain_2" xlink:title="definition: FinancialInstrumentPerformanceStatusAxis to FinancialInstrumentPerformanceStatusDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PerformingFinancingReceivableMember" xlink:label="PerformingFinancingReceivableMember" xlink:title="PerformingFinancingReceivableMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancialInstrumentPerformanceStatusDomain" xlink:to="PerformingFinancingReceivableMember" xlink:title="definition: FinancialInstrumentPerformanceStatusDomain to PerformingFinancingReceivableMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NonperformingFinancingReceivableMember" xlink:label="NonperformingFinancingReceivableMember" xlink:title="NonperformingFinancingReceivableMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancialInstrumentPerformanceStatusDomain" xlink:to="NonperformingFinancingReceivableMember" xlink:title="definition: FinancialInstrumentPerformanceStatusDomain to NonperformingFinancingReceivableMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:label="AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:title="AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:title="definition: ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable to AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ReceivableTypeDomain" xlink:label="ReceivableTypeDomain" xlink:title="ReceivableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="ReceivableTypeDomain" xlink:title="definition: AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis to ReceivableTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ReceivableTypeDomain" xlink:label="ReceivableTypeDomain_2" xlink:title="ReceivableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="ReceivableTypeDomain_2" xlink:title="definition: AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis to ReceivableTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_LegacyLoanMember" xlink:label="LegacyLoanMember" xlink:title="LegacyLoanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ReceivableTypeDomain" xlink:to="LegacyLoanMember" xlink:title="definition: ReceivableTypeDomain to LegacyLoanMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_AcquiredLoansMember" xlink:label="AcquiredLoansMember" xlink:title="AcquiredLoansMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ReceivableTypeDomain" xlink:to="AcquiredLoansMember" xlink:title="definition: ReceivableTypeDomain to AcquiredLoansMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/LoansSummaryOfImpairedLoansExcludingPurchasedImpairedDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/LoansTroubledDebtRestructuringsTdrsDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableModificationsLineItems" xlink:label="FinancingReceivableModificationsLineItems" xlink:title="FinancingReceivableModificationsLineItems" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_TroubledDebtRestructuringsAbstract" xlink:label="TroubledDebtRestructuringsAbstract" xlink:title="TroubledDebtRestructuringsAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableModificationsLineItems" xlink:to="TroubledDebtRestructuringsAbstract" xlink:title="definition: FinancingReceivableModificationsLineItems to TroubledDebtRestructuringsAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_FinancingReceivableModificationsCollectivelyEvaluatedForImpairmentThresholdBalance" xlink:label="FinancingReceivableModificationsCollectivelyEvaluatedForImpairmentThresholdBalance" xlink:title="FinancingReceivableModificationsCollectivelyEvaluatedForImpairmentThresholdBalance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableModificationsLineItems" xlink:to="FinancingReceivableModificationsCollectivelyEvaluatedForImpairmentThresholdBalance" xlink:title="definition: FinancingReceivableModificationsLineItems to FinancingReceivableModificationsCollectivelyEvaluatedForImpairmentThresholdBalance" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_FinancingReceivableIndividuallyEvaluatedForImpairmentThresholdBalance" xlink:label="FinancingReceivableIndividuallyEvaluatedForImpairmentThresholdBalance" xlink:title="FinancingReceivableIndividuallyEvaluatedForImpairmentThresholdBalance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableModificationsLineItems" xlink:to="FinancingReceivableIndividuallyEvaluatedForImpairmentThresholdBalance" xlink:title="definition: FinancingReceivableModificationsLineItems to FinancingReceivableIndividuallyEvaluatedForImpairmentThresholdBalance" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_FinancingReceivableModificationsNumberOfContracts" xlink:label="FinancingReceivableModificationsNumberOfContracts" xlink:title="FinancingReceivableModificationsNumberOfContracts" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableModificationsLineItems" xlink:to="FinancingReceivableModificationsNumberOfContracts" xlink:title="definition: FinancingReceivableModificationsLineItems to FinancingReceivableModificationsNumberOfContracts" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableModificationsRecordedInvestment" xlink:label="FinancingReceivableModificationsRecordedInvestment" xlink:title="FinancingReceivableModificationsRecordedInvestment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableModificationsLineItems" xlink:to="FinancingReceivableModificationsRecordedInvestment" xlink:title="definition: FinancingReceivableModificationsLineItems to FinancingReceivableModificationsRecordedInvestment" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableModificationsNumberOfContracts2" xlink:label="FinancingReceivableModificationsNumberOfContracts2" xlink:title="FinancingReceivableModificationsNumberOfContracts2" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableModificationsLineItems" xlink:to="FinancingReceivableModificationsNumberOfContracts2" xlink:title="definition: FinancingReceivableModificationsLineItems to FinancingReceivableModificationsNumberOfContracts2" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2" xlink:label="FinancingReceivableModificationsPostModificationRecordedInvestment2" xlink:title="FinancingReceivableModificationsPostModificationRecordedInvestment2" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableModificationsLineItems" xlink:to="FinancingReceivableModificationsPostModificationRecordedInvestment2" xlink:title="definition: FinancingReceivableModificationsLineItems to FinancingReceivableModificationsPostModificationRecordedInvestment2" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable" xlink:label="ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable" xlink:title="ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FinancingReceivableModificationsLineItems" xlink:to="ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable" xlink:title="definition: FinancingReceivableModificationsLineItems to ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable" order="8.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="FinancingReceivablePortfolioSegmentAxis" xlink:title="FinancingReceivablePortfolioSegmentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable" xlink:to="FinancingReceivablePortfolioSegmentAxis" xlink:title="definition: ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable to FinancingReceivablePortfolioSegmentAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="FinancingReceivablePortfolioSegmentDomain" xlink:title="FinancingReceivablePortfolioSegmentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancingReceivablePortfolioSegmentAxis" xlink:to="FinancingReceivablePortfolioSegmentDomain" xlink:title="definition: FinancingReceivablePortfolioSegmentAxis to FinancingReceivablePortfolioSegmentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="FinancingReceivablePortfolioSegmentDomain_2" xlink:title="FinancingReceivablePortfolioSegmentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancingReceivablePortfolioSegmentAxis" xlink:to="FinancingReceivablePortfolioSegmentDomain_2" xlink:title="definition: FinancingReceivablePortfolioSegmentAxis to FinancingReceivablePortfolioSegmentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="CommercialPortfolioSegmentMember" xlink:title="CommercialPortfolioSegmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivablePortfolioSegmentDomain" xlink:to="CommercialPortfolioSegmentMember" xlink:title="definition: FinancingReceivablePortfolioSegmentDomain to CommercialPortfolioSegmentMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ResidentialPortfolioSegmentMember" xlink:label="ResidentialPortfolioSegmentMember" xlink:title="ResidentialPortfolioSegmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivablePortfolioSegmentDomain" xlink:to="ResidentialPortfolioSegmentMember" xlink:title="definition: FinancingReceivablePortfolioSegmentDomain to ResidentialPortfolioSegmentMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:label="ConsumerPortfolioSegmentMember" xlink:title="ConsumerPortfolioSegmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivablePortfolioSegmentDomain" xlink:to="ConsumerPortfolioSegmentMember" xlink:title="definition: FinancingReceivablePortfolioSegmentDomain to ConsumerPortfolioSegmentMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:title="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable" xlink:to="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:title="definition: ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable to FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:title="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:title="definition: FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis to FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" xlink:title="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" xlink:title="definition: FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis to FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommercialLoanMember" xlink:label="CommercialLoanMember" xlink:title="CommercialLoanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="CommercialLoanMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to CommercialLoanMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ResidentialMortgageMember" xlink:label="ResidentialMortgageMember" xlink:title="ResidentialMortgageMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="ResidentialMortgageMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to ResidentialMortgageMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_ConsumerInstallmentIndirectMember" xlink:label="ConsumerInstallmentIndirectMember" xlink:title="ConsumerInstallmentIndirectMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="ConsumerInstallmentIndirectMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to ConsumerInstallmentIndirectMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_ConsumerInstallmentDirectMember" xlink:label="ConsumerInstallmentDirectMember" xlink:title="ConsumerInstallmentDirectMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="ConsumerInstallmentDirectMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to ConsumerInstallmentDirectMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_HomeEquityReceivablesMember" xlink:label="HomeEquityReceivablesMember" xlink:title="HomeEquityReceivablesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="HomeEquityReceivablesMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to HomeEquityReceivablesMember" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:label="AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:title="AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable" xlink:to="AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:title="definition: ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable to AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ReceivableTypeDomain" xlink:label="ReceivableTypeDomain" xlink:title="ReceivableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="ReceivableTypeDomain" xlink:title="definition: AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis to ReceivableTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ReceivableTypeDomain" xlink:label="ReceivableTypeDomain_2" xlink:title="ReceivableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis" xlink:to="ReceivableTypeDomain_2" xlink:title="definition: AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis to ReceivableTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_NonaccrualTDRsMember" xlink:label="NonaccrualTDRsMember" xlink:title="NonaccrualTDRsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ReceivableTypeDomain" xlink:to="NonaccrualTDRsMember" xlink:title="definition: ReceivableTypeDomain to NonaccrualTDRsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_AccruingTDRsMember" xlink:label="AccruingTDRsMember" xlink:title="AccruingTDRsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ReceivableTypeDomain" xlink:to="AccruingTDRsMember" xlink:title="definition: ReceivableTypeDomain to AccruingTDRsMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable" xlink:to="RangeAxis" xlink:title="definition: ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable to RangeAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeMember" xlink:label="RangeMember_2" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember_2" xlink:title="definition: RangeAxis to RangeMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_MinimumMember" xlink:label="MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MinimumMember" xlink:title="definition: RangeMember to MinimumMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_MaximumMember" xlink:label="MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MaximumMember" xlink:title="definition: RangeMember to MaximumMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/LoansAllowanceForLoanLossesDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:label="FinancingReceivableAllowanceForCreditLossesLineItems" xlink:title="FinancingReceivableAllowanceForCreditLossesLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AllowanceForLoanAndLeaseLossesRollForward" xlink:label="AllowanceForLoanAndLeaseLossesRollForward" xlink:title="AllowanceForLoanAndLeaseLossesRollForward" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="AllowanceForLoanAndLeaseLossesRollForward" xlink:title="definition: FinancingReceivableAllowanceForCreditLossesLineItems to AllowanceForLoanAndLeaseLossesRollForward" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LoansAndLeasesReceivableAllowance" xlink:label="LoansAndLeasesReceivableAllowance" xlink:title="LoansAndLeasesReceivableAllowance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="LoansAndLeasesReceivableAllowance" xlink:title="definition: FinancingReceivableAllowanceForCreditLossesLineItems to LoansAndLeasesReceivableAllowance" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs" xlink:label="AllowanceForLoanAndLeaseLossesWriteOffs" xlink:title="AllowanceForLoanAndLeaseLossesWriteOffs" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="AllowanceForLoanAndLeaseLossesWriteOffs" xlink:title="definition: FinancingReceivableAllowanceForCreditLossesLineItems to AllowanceForLoanAndLeaseLossesWriteOffs" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts" xlink:label="AllowanceForLoanAndLeaseLossRecoveryOfBadDebts" xlink:title="AllowanceForLoanAndLeaseLossRecoveryOfBadDebts" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="AllowanceForLoanAndLeaseLossRecoveryOfBadDebts" xlink:title="definition: FinancingReceivableAllowanceForCreditLossesLineItems to AllowanceForLoanAndLeaseLossRecoveryOfBadDebts" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ProvisionForLoanAndLeaseLosses" xlink:label="ProvisionForLoanAndLeaseLosses" xlink:title="ProvisionForLoanAndLeaseLosses" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="ProvisionForLoanAndLeaseLosses" xlink:title="definition: FinancingReceivableAllowanceForCreditLossesLineItems to ProvisionForLoanAndLeaseLosses" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:label="ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:title="ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:title="definition: FinancingReceivableAllowanceForCreditLossesLineItems to ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" order="6.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="FinancingReceivablePortfolioSegmentAxis" xlink:title="FinancingReceivablePortfolioSegmentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="FinancingReceivablePortfolioSegmentAxis" xlink:title="definition: ScheduleOfFinancingReceivableAllowanceForCreditLossesTable to FinancingReceivablePortfolioSegmentAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="FinancingReceivablePortfolioSegmentDomain" xlink:title="FinancingReceivablePortfolioSegmentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancingReceivablePortfolioSegmentAxis" xlink:to="FinancingReceivablePortfolioSegmentDomain" xlink:title="definition: FinancingReceivablePortfolioSegmentAxis to FinancingReceivablePortfolioSegmentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="FinancingReceivablePortfolioSegmentDomain_2" xlink:title="FinancingReceivablePortfolioSegmentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancingReceivablePortfolioSegmentAxis" xlink:to="FinancingReceivablePortfolioSegmentDomain_2" xlink:title="definition: FinancingReceivablePortfolioSegmentAxis to FinancingReceivablePortfolioSegmentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ResidentialPortfolioSegmentMember" xlink:label="ResidentialPortfolioSegmentMember" xlink:title="ResidentialPortfolioSegmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivablePortfolioSegmentDomain" xlink:to="ResidentialPortfolioSegmentMember" xlink:title="definition: FinancingReceivablePortfolioSegmentDomain to ResidentialPortfolioSegmentMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="CommercialPortfolioSegmentMember" xlink:title="CommercialPortfolioSegmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivablePortfolioSegmentDomain" xlink:to="CommercialPortfolioSegmentMember" xlink:title="definition: FinancingReceivablePortfolioSegmentDomain to CommercialPortfolioSegmentMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:label="ConsumerPortfolioSegmentMember" xlink:title="ConsumerPortfolioSegmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivablePortfolioSegmentDomain" xlink:to="ConsumerPortfolioSegmentMember" xlink:title="definition: FinancingReceivablePortfolioSegmentDomain to ConsumerPortfolioSegmentMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_UnallocatedFinancingReceivablesMember" xlink:label="UnallocatedFinancingReceivablesMember" xlink:title="UnallocatedFinancingReceivablesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivablePortfolioSegmentDomain" xlink:to="UnallocatedFinancingReceivablesMember" xlink:title="definition: FinancingReceivablePortfolioSegmentDomain to UnallocatedFinancingReceivablesMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:title="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:title="definition: ScheduleOfFinancingReceivableAllowanceForCreditLossesTable to FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:title="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:title="definition: FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis to FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" xlink:title="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" xlink:title="definition: FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis to FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommercialLoanMember" xlink:label="CommercialLoanMember" xlink:title="CommercialLoanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="CommercialLoanMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to CommercialLoanMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ResidentialMortgageMember" xlink:label="ResidentialMortgageMember" xlink:title="ResidentialMortgageMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="ResidentialMortgageMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to ResidentialMortgageMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_ConsumerInstallmentIndirectMember" xlink:label="ConsumerInstallmentIndirectMember" xlink:title="ConsumerInstallmentIndirectMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="ConsumerInstallmentIndirectMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to ConsumerInstallmentIndirectMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_ConsumerInstallmentDirectMember" xlink:label="ConsumerInstallmentDirectMember" xlink:title="ConsumerInstallmentDirectMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="ConsumerInstallmentDirectMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to ConsumerInstallmentDirectMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_HomeEquityReceivablesMember" xlink:label="HomeEquityReceivablesMember" xlink:title="HomeEquityReceivablesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="HomeEquityReceivablesMember" xlink:title="definition: FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain to HomeEquityReceivablesMember" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CreditLossStatusAxis" xlink:label="CreditLossStatusAxis" xlink:title="CreditLossStatusAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="CreditLossStatusAxis" xlink:title="definition: ScheduleOfFinancingReceivableAllowanceForCreditLossesTable to CreditLossStatusAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CreditLossStatusDomain" xlink:label="CreditLossStatusDomain" xlink:title="CreditLossStatusDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="CreditLossStatusAxis" xlink:to="CreditLossStatusDomain" xlink:title="definition: CreditLossStatusAxis to CreditLossStatusDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CreditLossStatusDomain" xlink:label="CreditLossStatusDomain_2" xlink:title="CreditLossStatusDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CreditLossStatusAxis" xlink:to="CreditLossStatusDomain_2" xlink:title="definition: CreditLossStatusAxis to CreditLossStatusDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancialAssetAcquiredWithCreditDeteriorationMember" xlink:label="FinancialAssetAcquiredWithCreditDeteriorationMember" xlink:title="FinancialAssetAcquiredWithCreditDeteriorationMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="CreditLossStatusDomain" xlink:to="FinancialAssetAcquiredWithCreditDeteriorationMember" xlink:title="definition: CreditLossStatusDomain to FinancialAssetAcquiredWithCreditDeteriorationMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/GoodwillAndIdentifiableIntangibleAssetsDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="FiniteLivedIntangibleAssetsLineItems" xlink:title="FiniteLivedIntangibleAssetsLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:label="FiniteLivedIntangibleAssetsNetAbstract" xlink:title="FiniteLivedIntangibleAssetsNetAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FiniteLivedIntangibleAssetsLineItems" xlink:to="FiniteLivedIntangibleAssetsNetAbstract" xlink:title="definition: FiniteLivedIntangibleAssetsLineItems to FiniteLivedIntangibleAssetsNetAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="FiniteLivedIntangibleAssetsGross" xlink:title="FiniteLivedIntangibleAssetsGross" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FiniteLivedIntangibleAssetsLineItems" xlink:to="FiniteLivedIntangibleAssetsGross" xlink:title="definition: FiniteLivedIntangibleAssetsLineItems to FiniteLivedIntangibleAssetsGross" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:title="FiniteLivedIntangibleAssetsAccumulatedAmortization" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FiniteLivedIntangibleAssetsLineItems" xlink:to="FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:title="definition: FiniteLivedIntangibleAssetsLineItems to FiniteLivedIntangibleAssetsAccumulatedAmortization" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="FiniteLivedIntangibleAssetsNet" xlink:title="FiniteLivedIntangibleAssetsNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FiniteLivedIntangibleAssetsLineItems" xlink:to="FiniteLivedIntangibleAssetsNet" xlink:title="definition: FiniteLivedIntangibleAssetsLineItems to FiniteLivedIntangibleAssetsNet" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:title="ScheduleOfFiniteLivedIntangibleAssetsTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FiniteLivedIntangibleAssetsLineItems" xlink:to="ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:title="definition: FiniteLivedIntangibleAssetsLineItems to ScheduleOfFiniteLivedIntangibleAssetsTable" order="5.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="FiniteLivedIntangibleAssetsByMajorClassAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:to="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="definition: ScheduleOfFiniteLivedIntangibleAssetsTable to FiniteLivedIntangibleAssetsByMajorClassAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="FiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="definition: FiniteLivedIntangibleAssetsByMajorClassAxis to FiniteLivedIntangibleAssetsMajorClassNameDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="FiniteLivedIntangibleAssetsMajorClassNameDomain_2" xlink:title="FiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="FiniteLivedIntangibleAssetsMajorClassNameDomain_2" xlink:title="definition: FiniteLivedIntangibleAssetsByMajorClassAxis to FiniteLivedIntangibleAssetsMajorClassNameDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CoreDepositsMember" xlink:label="CoreDepositsMember" xlink:title="CoreDepositsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="CoreDepositsMember" xlink:title="definition: FiniteLivedIntangibleAssetsMajorClassNameDomain to CoreDepositsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherIntangibleAssetsMember" xlink:label="OtherIntangibleAssetsMember" xlink:title="OtherIntangibleAssetsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="OtherIntangibleAssetsMember" xlink:title="definition: FiniteLivedIntangibleAssetsMajorClassNameDomain to OtherIntangibleAssetsMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/GoodwillAndIdentifiableIntangibleAssetsDetailsCalc2" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/MandatorilyRedeemablePreferredSecuritiesDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="DebtInstrumentLineItems" xlink:title="DebtInstrumentLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LongTermDebtByComponentsCurrentAndNoncurrentAlternativeAbstract" xlink:label="LongTermDebtByComponentsCurrentAndNoncurrentAlternativeAbstract" xlink:title="LongTermDebtByComponentsCurrentAndNoncurrentAlternativeAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="LongTermDebtByComponentsCurrentAndNoncurrentAlternativeAbstract" xlink:title="definition: DebtInstrumentLineItems to LongTermDebtByComponentsCurrentAndNoncurrentAlternativeAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrustAbstract" xlink:label="JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrustAbstract" xlink:title="JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrustAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrustAbstract" xlink:title="definition: DebtInstrumentLineItems to JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrustAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentIssuanceDate1" xlink:label="DebtInstrumentIssuanceDate1" xlink:title="DebtInstrumentIssuanceDate1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentIssuanceDate1" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentIssuanceDate1" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="DebtInstrumentFaceAmount" xlink:title="DebtInstrumentFaceAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentFaceAmount" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentFaceAmount" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_DebtInstrumentTermOfVariableRate" xlink:label="DebtInstrumentTermOfVariableRate" xlink:title="DebtInstrumentTermOfVariableRate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentTermOfVariableRate" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentTermOfVariableRate" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" xlink:label="DebtInstrumentDescriptionOfVariableRateBasis" xlink:title="DebtInstrumentDescriptionOfVariableRateBasis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentDescriptionOfVariableRateBasis" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentDescriptionOfVariableRateBasis" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:label="DebtInstrumentBasisSpreadOnVariableRate1" xlink:title="DebtInstrumentBasisSpreadOnVariableRate1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentBasisSpreadOnVariableRate1" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentBasisSpreadOnVariableRate1" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage" xlink:label="DebtInstrumentInterestRateEffectivePercentage" xlink:title="DebtInstrumentInterestRateEffectivePercentage" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentInterestRateEffectivePercentage" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentInterestRateEffectivePercentage" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentMaturityDate" xlink:label="DebtInstrumentMaturityDate" xlink:title="DebtInstrumentMaturityDate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentMaturityDate" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentMaturityDate" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentCallFeature" xlink:label="DebtInstrumentCallFeature" xlink:title="DebtInstrumentCallFeature" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentCallFeature" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentCallFeature" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_NumberOfUnconsolidatedSubsidiaryBusinessTrustsOwned" xlink:label="NumberOfUnconsolidatedSubsidiaryBusinessTrustsOwned" xlink:title="NumberOfUnconsolidatedSubsidiaryBusinessTrustsOwned" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="NumberOfUnconsolidatedSubsidiaryBusinessTrustsOwned" xlink:title="definition: DebtInstrumentLineItems to NumberOfUnconsolidatedSubsidiaryBusinessTrustsOwned" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage" xlink:label="EquityMethodInvestmentOwnershipPercentage" xlink:title="EquityMethodInvestmentOwnershipPercentage" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="EquityMethodInvestmentOwnershipPercentage" xlink:title="definition: DebtInstrumentLineItems to EquityMethodInvestmentOwnershipPercentage" order="12.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_ProceedsFromRedemptionOfDebenturesAndPreferredSecurities" xlink:label="ProceedsFromRedemptionOfDebenturesAndPreferredSecurities" xlink:title="ProceedsFromRedemptionOfDebenturesAndPreferredSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="ProceedsFromRedemptionOfDebenturesAndPreferredSecurities" xlink:title="definition: DebtInstrumentLineItems to ProceedsFromRedemptionOfDebenturesAndPreferredSecurities" order="13.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="DebtInstrumentTable" xlink:title="DebtInstrumentTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentTable" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentTable" order="14.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="LongtermDebtTypeAxis" xlink:title="LongtermDebtTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DebtInstrumentTable" xlink:to="LongtermDebtTypeAxis" xlink:title="definition: DebtInstrumentTable to LongtermDebtTypeAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="LongtermDebtTypeDomain" xlink:title="LongtermDebtTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="LongtermDebtTypeAxis" xlink:to="LongtermDebtTypeDomain" xlink:title="definition: LongtermDebtTypeAxis to LongtermDebtTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="LongtermDebtTypeDomain_2" xlink:title="LongtermDebtTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="LongtermDebtTypeAxis" xlink:to="LongtermDebtTypeDomain_2" xlink:title="definition: LongtermDebtTypeAxis to LongtermDebtTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SeniorNotesMember" xlink:label="SeniorNotesMember" xlink:title="SeniorNotesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LongtermDebtTypeDomain" xlink:to="SeniorNotesMember" xlink:title="definition: LongtermDebtTypeDomain to SeniorNotesMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2018/dei-2018-01-31.xsd#dei_LegalEntityAxis" xlink:label="LegalEntityAxis" xlink:title="LegalEntityAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DebtInstrumentTable" xlink:to="LegalEntityAxis" xlink:title="definition: DebtInstrumentTable to LegalEntityAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2018/dei-2018-01-31.xsd#dei_EntityDomain" xlink:label="EntityDomain" xlink:title="EntityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="LegalEntityAxis" xlink:to="EntityDomain" xlink:title="definition: LegalEntityAxis to EntityDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2018/dei-2018-01-31.xsd#dei_EntityDomain" xlink:label="EntityDomain_2" xlink:title="EntityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="LegalEntityAxis" xlink:to="EntityDomain_2" xlink:title="definition: LegalEntityAxis to EntityDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_CommunityStatutoryTrust3Member" xlink:label="CommunityStatutoryTrust3Member" xlink:title="CommunityStatutoryTrust3Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EntityDomain" xlink:to="CommunityStatutoryTrust3Member" xlink:title="definition: EntityDomain to CommunityStatutoryTrust3Member" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_CommunityStatutoryTrust4Member" xlink:label="CommunityStatutoryTrust4Member" xlink:title="CommunityStatutoryTrust4Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EntityDomain" xlink:to="CommunityStatutoryTrust4Member" xlink:title="definition: EntityDomain to CommunityStatutoryTrust4Member" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_MBVTStatutoryTrustIMember" xlink:label="MBVTStatutoryTrustIMember" xlink:title="MBVTStatutoryTrustIMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EntityDomain" xlink:to="MBVTStatutoryTrustIMember" xlink:title="definition: EntityDomain to MBVTStatutoryTrustIMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_VariableRateAxis" xlink:label="VariableRateAxis" xlink:title="VariableRateAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DebtInstrumentTable" xlink:to="VariableRateAxis" xlink:title="definition: DebtInstrumentTable to VariableRateAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="VariableRateDomain" xlink:title="VariableRateDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="VariableRateAxis" xlink:to="VariableRateDomain" xlink:title="definition: VariableRateAxis to VariableRateDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="VariableRateDomain_2" xlink:title="VariableRateDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="VariableRateAxis" xlink:to="VariableRateDomain_2" xlink:title="definition: VariableRateAxis to VariableRateDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:label="LondonInterbankOfferedRateLIBORMember" xlink:title="LondonInterbankOfferedRateLIBORMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="VariableRateDomain" xlink:to="LondonInterbankOfferedRateLIBORMember" xlink:title="definition: VariableRateDomain to LondonInterbankOfferedRateLIBORMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="SubsequentEventTypeAxis" xlink:title="SubsequentEventTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DebtInstrumentTable" xlink:to="SubsequentEventTypeAxis" xlink:title="definition: DebtInstrumentTable to SubsequentEventTypeAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain_2" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain_2" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="SubsequentEventMember" xlink:title="SubsequentEventMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventTypeDomain" xlink:to="SubsequentEventMember" xlink:title="definition: SubsequentEventTypeDomain to SubsequentEventMember" order="1.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/BenefitPlansDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:label="DefinedBenefitPlanDisclosureLineItems" xlink:title="DefinedBenefitPlanDisclosureLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DefinedBenefitPlanAdditionalInformationAbstract" xlink:label="DefinedBenefitPlanAdditionalInformationAbstract" xlink:title="DefinedBenefitPlanAdditionalInformationAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DefinedBenefitPlanDisclosureLineItems" xlink:to="DefinedBenefitPlanAdditionalInformationAbstract" xlink:title="definition: DefinedBenefitPlanDisclosureLineItems to DefinedBenefitPlanAdditionalInformationAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract" xlink:label="DefinedBenefitPlanNetPeriodicBenefitCostAbstract" xlink:title="DefinedBenefitPlanNetPeriodicBenefitCostAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DefinedBenefitPlanDisclosureLineItems" xlink:to="DefinedBenefitPlanNetPeriodicBenefitCostAbstract" xlink:title="definition: DefinedBenefitPlanDisclosureLineItems to DefinedBenefitPlanNetPeriodicBenefitCostAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DefinedBenefitPlanServiceCost" xlink:label="DefinedBenefitPlanServiceCost" xlink:title="DefinedBenefitPlanServiceCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DefinedBenefitPlanDisclosureLineItems" xlink:to="DefinedBenefitPlanServiceCost" xlink:title="definition: DefinedBenefitPlanDisclosureLineItems to DefinedBenefitPlanServiceCost" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DefinedBenefitPlanInterestCost" xlink:label="DefinedBenefitPlanInterestCost" xlink:title="DefinedBenefitPlanInterestCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DefinedBenefitPlanDisclosureLineItems" xlink:to="DefinedBenefitPlanInterestCost" xlink:title="definition: DefinedBenefitPlanDisclosureLineItems to DefinedBenefitPlanInterestCost" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets" xlink:label="DefinedBenefitPlanExpectedReturnOnPlanAssets" xlink:title="DefinedBenefitPlanExpectedReturnOnPlanAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DefinedBenefitPlanDisclosureLineItems" xlink:to="DefinedBenefitPlanExpectedReturnOnPlanAssets" xlink:title="definition: DefinedBenefitPlanDisclosureLineItems to DefinedBenefitPlanExpectedReturnOnPlanAssets" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses" xlink:label="DefinedBenefitPlanAmortizationOfGainsLosses" xlink:title="DefinedBenefitPlanAmortizationOfGainsLosses" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DefinedBenefitPlanDisclosureLineItems" xlink:to="DefinedBenefitPlanAmortizationOfGainsLosses" xlink:title="definition: DefinedBenefitPlanDisclosureLineItems to DefinedBenefitPlanAmortizationOfGainsLosses" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit" xlink:label="DefinedBenefitPlanAmortizationOfPriorServiceCostCredit" xlink:title="DefinedBenefitPlanAmortizationOfPriorServiceCostCredit" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DefinedBenefitPlanDisclosureLineItems" xlink:to="DefinedBenefitPlanAmortizationOfPriorServiceCostCredit" xlink:title="definition: DefinedBenefitPlanDisclosureLineItems to DefinedBenefitPlanAmortizationOfPriorServiceCostCredit" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost" xlink:label="DefinedBenefitPlanNetPeriodicBenefitCost" xlink:title="DefinedBenefitPlanNetPeriodicBenefitCost" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DefinedBenefitPlanDisclosureLineItems" xlink:to="DefinedBenefitPlanNetPeriodicBenefitCost" xlink:title="definition: DefinedBenefitPlanDisclosureLineItems to DefinedBenefitPlanNetPeriodicBenefitCost" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DefinedBenefitPlanTaxStatusExtensibleList" xlink:label="DefinedBenefitPlanTaxStatusExtensibleList" xlink:title="DefinedBenefitPlanTaxStatusExtensibleList" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DefinedBenefitPlanDisclosureLineItems" xlink:to="DefinedBenefitPlanTaxStatusExtensibleList" xlink:title="definition: DefinedBenefitPlanDisclosureLineItems to DefinedBenefitPlanTaxStatusExtensibleList" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesAfterTax" xlink:label="DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesAfterTax" xlink:title="DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesAfterTax" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DefinedBenefitPlanDisclosureLineItems" xlink:to="DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesAfterTax" xlink:title="definition: DefinedBenefitPlanDisclosureLineItems to DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesAfterTax" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate" xlink:label="DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate" xlink:title="DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DefinedBenefitPlanDisclosureLineItems" xlink:to="DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate" xlink:title="definition: DefinedBenefitPlanDisclosureLineItems to DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate" order="11.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:label="ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:title="ScheduleOfDefinedBenefitPlansDisclosuresTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="DefinedBenefitPlanDisclosureLineItems" xlink:to="ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:title="definition: DefinedBenefitPlanDisclosureLineItems to ScheduleOfDefinedBenefitPlansDisclosuresTable" order="12.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RetirementPlanTypeAxis" xlink:label="RetirementPlanTypeAxis" xlink:title="RetirementPlanTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="RetirementPlanTypeAxis" xlink:title="definition: ScheduleOfDefinedBenefitPlansDisclosuresTable to RetirementPlanTypeAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="RetirementPlanTypeDomain" xlink:title="RetirementPlanTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RetirementPlanTypeAxis" xlink:to="RetirementPlanTypeDomain" xlink:title="definition: RetirementPlanTypeAxis to RetirementPlanTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="RetirementPlanTypeDomain_2" xlink:title="RetirementPlanTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RetirementPlanTypeAxis" xlink:to="RetirementPlanTypeDomain_2" xlink:title="definition: RetirementPlanTypeAxis to RetirementPlanTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PensionPlansDefinedBenefitMember" xlink:label="PensionPlansDefinedBenefitMember" xlink:title="PensionPlansDefinedBenefitMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RetirementPlanTypeDomain" xlink:to="PensionPlansDefinedBenefitMember" xlink:title="definition: RetirementPlanTypeDomain to PensionPlansDefinedBenefitMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember" xlink:label="OtherPostretirementBenefitPlansDefinedBenefitMember" xlink:title="OtherPostretirementBenefitPlansDefinedBenefitMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RetirementPlanTypeDomain" xlink:to="OtherPostretirementBenefitPlansDefinedBenefitMember" xlink:title="definition: RetirementPlanTypeDomain to OtherPostretirementBenefitPlansDefinedBenefitMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/EarningsPerShareDetails" />
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/CommitmentsContingentLiabilitiesAndRestrictionsDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:label="FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:title="FairValueOffBalanceSheetRisksDisclosureInformationLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LossContingencyEstimateAbstract" xlink:label="LossContingencyEstimateAbstract" xlink:title="LossContingencyEstimateAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="LossContingencyEstimateAbstract" xlink:title="definition: FairValueOffBalanceSheetRisksDisclosureInformationLineItems to LossContingencyEstimateAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability" xlink:label="FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability" xlink:title="FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability" xlink:title="definition: FairValueOffBalanceSheetRisksDisclosureInformationLineItems to FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LossContingencyEstimateOfPossibleLoss" xlink:label="LossContingencyEstimateOfPossibleLoss" xlink:title="LossContingencyEstimateOfPossibleLoss" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="LossContingencyEstimateOfPossibleLoss" xlink:title="definition: FairValueOffBalanceSheetRisksDisclosureInformationLineItems to LossContingencyEstimateOfPossibleLoss" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:label="ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:title="ScheduleOfFairValueOffBalanceSheetRisksTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:title="definition: FairValueOffBalanceSheetRisksDisclosureInformationLineItems to ScheduleOfFairValueOffBalanceSheetRisksTable" order="4.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="FinancialInstrumentAxis" xlink:title="FinancialInstrumentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:to="FinancialInstrumentAxis" xlink:title="definition: ScheduleOfFairValueOffBalanceSheetRisksTable to FinancialInstrumentAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CommitmentsToExtendCreditMember" xlink:label="CommitmentsToExtendCreditMember" xlink:title="CommitmentsToExtendCreditMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="CommitmentsToExtendCreditMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to CommitmentsToExtendCreditMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StandbyLettersOfCreditMember" xlink:label="StandbyLettersOfCreditMember" xlink:title="StandbyLettersOfCreditMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="StandbyLettersOfCreditMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to StandbyLettersOfCreditMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:to="RangeAxis" xlink:title="definition: ScheduleOfFairValueOffBalanceSheetRisksTable to RangeAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeMember" xlink:label="RangeMember_2" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember_2" xlink:title="definition: RangeAxis to RangeMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_MinimumMember" xlink:label="MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MinimumMember" xlink:title="definition: RangeMember to MinimumMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_MaximumMember" xlink:label="MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MaximumMember" xlink:title="definition: RangeMember to MaximumMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/FairValueFinancialAssetsAndLiabilitiesAccountedForAtFairValueOnRecurringBasisDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAbstract" xlink:label="AvailableForSaleSecuritiesAbstract" xlink:title="AvailableForSaleSecuritiesAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="AvailableForSaleSecuritiesAbstract" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to AvailableForSaleSecuritiesAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_MortgagesHeldForSaleFairValueDisclosure" xlink:label="MortgagesHeldForSaleFairValueDisclosure" xlink:title="MortgagesHeldForSaleFairValueDisclosure" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="MortgagesHeldForSaleFairValueDisclosure" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to MortgagesHeldForSaleFairValueDisclosure" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeAssets" xlink:label="DerivativeAssets" xlink:title="DerivativeAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="DerivativeAssets" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to DerivativeAssets" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeLiabilities" xlink:label="DerivativeLiabilities" xlink:title="DerivativeLiabilities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="DerivativeLiabilities" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to DerivativeLiabilities" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueNetAssetLiability" xlink:label="FairValueNetAssetLiability" xlink:title="FairValueNetAssetLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="FairValueNetAssetLiability" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to FairValueNetAssetLiability" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_LoansHeldForSaleMortgagesPrincipalAmount" xlink:label="LoansHeldForSaleMortgagesPrincipalAmount" xlink:title="LoansHeldForSaleMortgagesPrincipalAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="LoansHeldForSaleMortgagesPrincipalAmount" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to LoansHeldForSaleMortgagesPrincipalAmount" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="AvailableForSaleSecuritiesDebtSecurities" xlink:title="AvailableForSaleSecuritiesDebtSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="AvailableForSaleSecuritiesDebtSecurities" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to AvailableForSaleSecuritiesDebtSecurities" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EquitySecuritiesFvNi" xlink:label="EquitySecuritiesFvNi" xlink:title="EquitySecuritiesFvNi" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="EquitySecuritiesFvNi" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to EquitySecuritiesFvNi" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecuritiesEquitySecurities" xlink:label="AvailableForSaleSecuritiesEquitySecurities" xlink:title="AvailableForSaleSecuritiesEquitySecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="AvailableForSaleSecuritiesEquitySecurities" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to AvailableForSaleSecuritiesEquitySecurities" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AvailableForSaleSecurities" xlink:label="AvailableForSaleSecurities" xlink:title="AvailableForSaleSecurities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="AvailableForSaleSecurities" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to AvailableForSaleSecurities" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" order="11.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="FairValueByMeasurementFrequencyAxis" xlink:title="FairValueByMeasurementFrequencyAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="FairValueByMeasurementFrequencyAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to FairValueByMeasurementFrequencyAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="FairValueMeasurementFrequencyDomain" xlink:title="FairValueMeasurementFrequencyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByMeasurementFrequencyAxis" xlink:to="FairValueMeasurementFrequencyDomain" xlink:title="definition: FairValueByMeasurementFrequencyAxis to FairValueMeasurementFrequencyDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="FairValueMeasurementFrequencyDomain_2" xlink:title="FairValueMeasurementFrequencyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByMeasurementFrequencyAxis" xlink:to="FairValueMeasurementFrequencyDomain_2" xlink:title="definition: FairValueByMeasurementFrequencyAxis to FairValueMeasurementFrequencyDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="FairValueMeasurementsRecurringMember" xlink:title="FairValueMeasurementsRecurringMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementFrequencyDomain" xlink:to="FairValueMeasurementsRecurringMember" xlink:title="definition: FairValueMeasurementFrequencyDomain to FairValueMeasurementsRecurringMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="FairValueByFairValueHierarchyLevelAxis" xlink:title="FairValueByFairValueHierarchyLevelAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="FairValueByFairValueHierarchyLevelAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to FairValueByFairValueHierarchyLevelAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="FairValueMeasurementsFairValueHierarchyDomain" xlink:title="FairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByFairValueHierarchyLevelAxis" xlink:to="FairValueMeasurementsFairValueHierarchyDomain" xlink:title="definition: FairValueByFairValueHierarchyLevelAxis to FairValueMeasurementsFairValueHierarchyDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="FairValueMeasurementsFairValueHierarchyDomain_2" xlink:title="FairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByFairValueHierarchyLevelAxis" xlink:to="FairValueMeasurementsFairValueHierarchyDomain_2" xlink:title="definition: FairValueByFairValueHierarchyLevelAxis to FairValueMeasurementsFairValueHierarchyDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="FairValueInputsLevel1Member" xlink:title="FairValueInputsLevel1Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementsFairValueHierarchyDomain" xlink:to="FairValueInputsLevel1Member" xlink:title="definition: FairValueMeasurementsFairValueHierarchyDomain to FairValueInputsLevel1Member" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="FairValueInputsLevel2Member" xlink:title="FairValueInputsLevel2Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementsFairValueHierarchyDomain" xlink:to="FairValueInputsLevel2Member" xlink:title="definition: FairValueMeasurementsFairValueHierarchyDomain to FairValueInputsLevel2Member" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="FairValueInputsLevel3Member" xlink:title="FairValueInputsLevel3Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementsFairValueHierarchyDomain" xlink:to="FairValueInputsLevel3Member" xlink:title="definition: FairValueMeasurementsFairValueHierarchyDomain to FairValueInputsLevel3Member" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="FinancialInstrumentAxis" xlink:title="FinancialInstrumentAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="FinancialInstrumentAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to FinancialInstrumentAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_USTreasuryAndGovernmentMember" xlink:label="USTreasuryAndGovernmentMember" xlink:title="USTreasuryAndGovernmentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="USTreasuryAndGovernmentMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to USTreasuryAndGovernmentMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember" xlink:label="USStatesAndPoliticalSubdivisionsMember" xlink:title="USStatesAndPoliticalSubdivisionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="USStatesAndPoliticalSubdivisionsMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to USStatesAndPoliticalSubdivisionsMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:label="MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:title="MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="CorporateDebtSecuritiesMember" xlink:title="CorporateDebtSecuritiesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="CorporateDebtSecuritiesMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to CorporateDebtSecuritiesMember" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_GovernmentAgencyCollateralizedMortgageObligationsMember" xlink:label="GovernmentAgencyCollateralizedMortgageObligationsMember" xlink:title="GovernmentAgencyCollateralizedMortgageObligationsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="GovernmentAgencyCollateralizedMortgageObligationsMember" xlink:title="definition: TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain to GovernmentAgencyCollateralizedMortgageObligationsMember" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="DerivativeInstrumentRiskAxis" xlink:title="DerivativeInstrumentRiskAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="DerivativeInstrumentRiskAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to DerivativeInstrumentRiskAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="DerivativeContractTypeDomain" xlink:title="DerivativeContractTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="DerivativeInstrumentRiskAxis" xlink:to="DerivativeContractTypeDomain" xlink:title="definition: DerivativeInstrumentRiskAxis to DerivativeContractTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="DerivativeContractTypeDomain_2" xlink:title="DerivativeContractTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="DerivativeInstrumentRiskAxis" xlink:to="DerivativeContractTypeDomain_2" xlink:title="definition: DerivativeInstrumentRiskAxis to DerivativeContractTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LoanOriginationCommitmentsMember" xlink:label="LoanOriginationCommitmentsMember" xlink:title="LoanOriginationCommitmentsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DerivativeContractTypeDomain" xlink:to="LoanOriginationCommitmentsMember" xlink:title="definition: DerivativeContractTypeDomain to LoanOriginationCommitmentsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ForwardContractsMember" xlink:label="ForwardContractsMember" xlink:title="ForwardContractsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DerivativeContractTypeDomain" xlink:to="ForwardContractsMember" xlink:title="definition: DerivativeContractTypeDomain to ForwardContractsMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_InterestRateSwapMember" xlink:label="InterestRateSwapMember" xlink:title="InterestRateSwapMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DerivativeContractTypeDomain" xlink:to="InterestRateSwapMember" xlink:title="definition: DerivativeContractTypeDomain to InterestRateSwapMember" order="3.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/FairValueAssetsAndLiabilitiesMeasuredOnNonrecurringBasisDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueMeasurementsNonrecurringValueMeasurementAbstract" xlink:label="FairValueMeasurementsNonrecurringValueMeasurementAbstract" xlink:title="FairValueMeasurementsNonrecurringValueMeasurementAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="FairValueMeasurementsNonrecurringValueMeasurementAbstract" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to FairValueMeasurementsNonrecurringValueMeasurementAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherRealEstate" xlink:label="OtherRealEstate" xlink:title="OtherRealEstate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="OtherRealEstate" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to OtherRealEstate" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ImpairedFinancingReceivableRelatedAllowance" xlink:label="ImpairedFinancingReceivableRelatedAllowance" xlink:title="ImpairedFinancingReceivableRelatedAllowance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="ImpairedFinancingReceivableRelatedAllowance" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to ImpairedFinancingReceivableRelatedAllowance" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" order="4.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="FairValueByMeasurementFrequencyAxis" xlink:title="FairValueByMeasurementFrequencyAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="FairValueByMeasurementFrequencyAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to FairValueByMeasurementFrequencyAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="FairValueMeasurementFrequencyDomain" xlink:title="FairValueMeasurementFrequencyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByMeasurementFrequencyAxis" xlink:to="FairValueMeasurementFrequencyDomain" xlink:title="definition: FairValueByMeasurementFrequencyAxis to FairValueMeasurementFrequencyDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="FairValueMeasurementFrequencyDomain_2" xlink:title="FairValueMeasurementFrequencyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByMeasurementFrequencyAxis" xlink:to="FairValueMeasurementFrequencyDomain_2" xlink:title="definition: FairValueByMeasurementFrequencyAxis to FairValueMeasurementFrequencyDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueMeasurementsNonrecurringMember" xlink:label="FairValueMeasurementsNonrecurringMember" xlink:title="FairValueMeasurementsNonrecurringMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementFrequencyDomain" xlink:to="FairValueMeasurementsNonrecurringMember" xlink:title="definition: FairValueMeasurementFrequencyDomain to FairValueMeasurementsNonrecurringMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="FairValueByFairValueHierarchyLevelAxis" xlink:title="FairValueByFairValueHierarchyLevelAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="FairValueByFairValueHierarchyLevelAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to FairValueByFairValueHierarchyLevelAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="FairValueMeasurementsFairValueHierarchyDomain" xlink:title="FairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByFairValueHierarchyLevelAxis" xlink:to="FairValueMeasurementsFairValueHierarchyDomain" xlink:title="definition: FairValueByFairValueHierarchyLevelAxis to FairValueMeasurementsFairValueHierarchyDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="FairValueMeasurementsFairValueHierarchyDomain_2" xlink:title="FairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByFairValueHierarchyLevelAxis" xlink:to="FairValueMeasurementsFairValueHierarchyDomain_2" xlink:title="definition: FairValueByFairValueHierarchyLevelAxis to FairValueMeasurementsFairValueHierarchyDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="FairValueInputsLevel1Member" xlink:title="FairValueInputsLevel1Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementsFairValueHierarchyDomain" xlink:to="FairValueInputsLevel1Member" xlink:title="definition: FairValueMeasurementsFairValueHierarchyDomain to FairValueInputsLevel1Member" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="FairValueInputsLevel2Member" xlink:title="FairValueInputsLevel2Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementsFairValueHierarchyDomain" xlink:to="FairValueInputsLevel2Member" xlink:title="definition: FairValueMeasurementsFairValueHierarchyDomain to FairValueInputsLevel2Member" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="FairValueInputsLevel3Member" xlink:title="FairValueInputsLevel3Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueMeasurementsFairValueHierarchyDomain" xlink:to="FairValueInputsLevel3Member" xlink:title="definition: FairValueMeasurementsFairValueHierarchyDomain to FairValueInputsLevel3Member" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueByAssetClassAxis" xlink:label="FairValueByAssetClassAxis" xlink:title="FairValueByAssetClassAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="FairValueByAssetClassAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to FairValueByAssetClassAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:label="FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:title="FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByAssetClassAxis" xlink:to="FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:title="definition: FairValueByAssetClassAxis to FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:label="FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_2" xlink:title="FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByAssetClassAxis" xlink:to="FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_2" xlink:title="definition: FairValueByAssetClassAxis to FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_OtherRealEstateOwnedMember" xlink:label="OtherRealEstateOwnedMember" xlink:title="OtherRealEstateOwnedMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:to="OtherRealEstateOwnedMember" xlink:title="definition: FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain to OtherRealEstateOwnedMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_MortgageServicingRightsMember" xlink:label="MortgageServicingRightsMember" xlink:title="MortgageServicingRightsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:to="MortgageServicingRightsMember" xlink:title="definition: FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain to MortgageServicingRightsMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="RangeAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to RangeAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeMember" xlink:label="RangeMember_2" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember_2" xlink:title="definition: RangeAxis to RangeMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_MinimumMember" xlink:label="MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MinimumMember" xlink:title="definition: RangeMember to MinimumMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_MaximumMember" xlink:label="MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MaximumMember" xlink:title="definition: RangeMember to MaximumMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/FairValueSignificantUnobservableInputsDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:label="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueInputsQuantitativeInformationAbstract" xlink:label="FairValueInputsQuantitativeInformationAbstract" xlink:title="FairValueInputsQuantitativeInformationAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="FairValueInputsQuantitativeInformationAbstract" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to FairValueInputsQuantitativeInformationAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherRealEstate" xlink:label="OtherRealEstate" xlink:title="OtherRealEstate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="OtherRealEstate" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to OtherRealEstate" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherRealEstateOwnedValuationTechniqueExtensibleList" xlink:label="OtherRealEstateOwnedValuationTechniqueExtensibleList" xlink:title="OtherRealEstateOwnedValuationTechniqueExtensibleList" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="OtherRealEstateOwnedValuationTechniqueExtensibleList" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to OtherRealEstateOwnedValuationTechniqueExtensibleList" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherRealEstateOwnedMeasurementInputExtensibleList" xlink:label="OtherRealEstateOwnedMeasurementInputExtensibleList" xlink:title="OtherRealEstateOwnedMeasurementInputExtensibleList" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="OtherRealEstateOwnedMeasurementInputExtensibleList" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to OtherRealEstateOwnedMeasurementInputExtensibleList" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherRealEstateOwnedMeasurementInput" xlink:label="OtherRealEstateOwnedMeasurementInput" xlink:title="OtherRealEstateOwnedMeasurementInput" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="OtherRealEstateOwnedMeasurementInput" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to OtherRealEstateOwnedMeasurementInput" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeAssets" xlink:label="DerivativeAssets" xlink:title="DerivativeAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="DerivativeAssets" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to DerivativeAssets" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeAssetValuationTechniqueExtensibleList" xlink:label="DerivativeAssetValuationTechniqueExtensibleList" xlink:title="DerivativeAssetValuationTechniqueExtensibleList" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="DerivativeAssetValuationTechniqueExtensibleList" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to DerivativeAssetValuationTechniqueExtensibleList" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeAssetMeasurementInputExtensibleList" xlink:label="DerivativeAssetMeasurementInputExtensibleList" xlink:title="DerivativeAssetMeasurementInputExtensibleList" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="DerivativeAssetMeasurementInputExtensibleList" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to DerivativeAssetMeasurementInputExtensibleList" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeAssetMeasurementInput" xlink:label="DerivativeAssetMeasurementInput" xlink:title="DerivativeAssetMeasurementInput" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="DerivativeAssetMeasurementInput" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to DerivativeAssetMeasurementInput" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:label="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems to FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" order="10.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="RangeAxis" xlink:title="definition: FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable to RangeAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_RangeMember" xlink:label="RangeMember_2" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember_2" xlink:title="definition: RangeAxis to RangeMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_MinimumMember" xlink:label="MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MinimumMember" xlink:title="definition: RangeMember to MinimumMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_MaximumMember" xlink:label="MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MaximumMember" xlink:title="definition: RangeMember to MaximumMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_WeightedAverageMember" xlink:label="WeightedAverageMember" xlink:title="WeightedAverageMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="WeightedAverageMember" xlink:title="definition: RangeMember to WeightedAverageMember" order="3.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/FairValueCarryingAmountsAndEstimatedFairValuesOfOtherFinancialInstrumentsDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:label="FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:title="FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:label="FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:title="FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:to="FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:title="definition: FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems to FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:label="FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:title="FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:to="FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:title="definition: FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems to FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DepositsFairValueDisclosure" xlink:label="DepositsFairValueDisclosure" xlink:title="DepositsFairValueDisclosure" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:to="DepositsFairValueDisclosure" xlink:title="definition: FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems to DepositsFairValueDisclosure" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_ShortTermDebtFairValueDisclosure" xlink:label="ShortTermDebtFairValueDisclosure" xlink:title="ShortTermDebtFairValueDisclosure" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:to="ShortTermDebtFairValueDisclosure" xlink:title="definition: FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems to ShortTermDebtFairValueDisclosure" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure" xlink:label="SecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure" xlink:title="SecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:to="SecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure" xlink:title="definition: FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems to SecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_OtherLongTermDebtFairValueDisclosure" xlink:label="OtherLongTermDebtFairValueDisclosure" xlink:title="OtherLongTermDebtFairValueDisclosure" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:to="OtherLongTermDebtFairValueDisclosure" xlink:title="definition: FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems to OtherLongTermDebtFairValueDisclosure" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations" xlink:label="FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations" xlink:title="FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:to="FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations" xlink:title="definition: FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems to FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_LoansReceivableFairValueDisclosure" xlink:label="LoansReceivableFairValueDisclosure" xlink:title="LoansReceivableFairValueDisclosure" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:to="LoansReceivableFairValueDisclosure" xlink:title="definition: FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems to LoansReceivableFairValueDisclosure" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueByBalanceSheetGroupingTable" xlink:label="FairValueByBalanceSheetGroupingTable" xlink:title="FairValueByBalanceSheetGroupingTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:to="FairValueByBalanceSheetGroupingTable" xlink:title="definition: FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems to FairValueByBalanceSheetGroupingTable" order="9.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="FairValueByMeasurementBasisAxis" xlink:title="FairValueByMeasurementBasisAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="FairValueByBalanceSheetGroupingTable" xlink:to="FairValueByMeasurementBasisAxis" xlink:title="definition: FairValueByBalanceSheetGroupingTable to FairValueByMeasurementBasisAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain" xlink:label="FairValueDisclosureItemAmountsDomain" xlink:title="FairValueDisclosureItemAmountsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="FairValueByMeasurementBasisAxis" xlink:to="FairValueDisclosureItemAmountsDomain" xlink:title="definition: FairValueByMeasurementBasisAxis to FairValueDisclosureItemAmountsDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="PortionAtFairValueFairValueDisclosureMember" xlink:title="PortionAtFairValueFairValueDisclosureMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueDisclosureItemAmountsDomain" xlink:to="PortionAtFairValueFairValueDisclosureMember" xlink:title="definition: FairValueDisclosureItemAmountsDomain to PortionAtFairValueFairValueDisclosureMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="PortionAtFairValueFairValueDisclosureMember_2" xlink:title="PortionAtFairValueFairValueDisclosureMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByMeasurementBasisAxis" xlink:to="PortionAtFairValueFairValueDisclosureMember_2" xlink:title="definition: FairValueByMeasurementBasisAxis to PortionAtFairValueFairValueDisclosureMember_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:label="CarryingReportedAmountFairValueDisclosureMember" xlink:title="CarryingReportedAmountFairValueDisclosureMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueDisclosureItemAmountsDomain" xlink:to="CarryingReportedAmountFairValueDisclosureMember" xlink:title="definition: FairValueDisclosureItemAmountsDomain to CarryingReportedAmountFairValueDisclosureMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="EstimateOfFairValueFairValueDisclosureMember" xlink:title="EstimateOfFairValueFairValueDisclosureMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="FairValueDisclosureItemAmountsDomain" xlink:to="EstimateOfFairValueFairValueDisclosureMember" xlink:title="definition: FairValueDisclosureItemAmountsDomain to EstimateOfFairValueFairValueDisclosureMember" order="3.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/DerivativeInstrumentsDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeLineItems" xlink:label="DerivativeLineItems" xlink:title="DerivativeLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeInstrumentDetailAbstract" xlink:label="DerivativeInstrumentDetailAbstract" xlink:title="DerivativeInstrumentDetailAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DerivativeLineItems" xlink:to="DerivativeInstrumentDetailAbstract" xlink:title="definition: DerivativeLineItems to DerivativeInstrumentDetailAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_DerivativeNotionalAmount" xlink:label="DerivativeNotionalAmount" xlink:title="DerivativeNotionalAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DerivativeLineItems" xlink:to="DerivativeNotionalAmount" xlink:title="definition: DerivativeLineItems to DerivativeNotionalAmount" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeVariableInterestRate" xlink:label="DerivativeVariableInterestRate" xlink:title="DerivativeVariableInterestRate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DerivativeLineItems" xlink:to="DerivativeVariableInterestRate" xlink:title="definition: DerivativeLineItems to DerivativeVariableInterestRate" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeFixedInterestRate" xlink:label="DerivativeFixedInterestRate" xlink:title="DerivativeFixedInterestRate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DerivativeLineItems" xlink:to="DerivativeFixedInterestRate" xlink:title="definition: DerivativeLineItems to DerivativeFixedInterestRate" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeTermOfContract" xlink:label="DerivativeTermOfContract" xlink:title="DerivativeTermOfContract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DerivativeLineItems" xlink:to="DerivativeTermOfContract" xlink:title="definition: DerivativeLineItems to DerivativeTermOfContract" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeLiabilityFairValueGrossAsset" xlink:label="DerivativeLiabilityFairValueGrossAsset" xlink:title="DerivativeLiabilityFairValueGrossAsset" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DerivativeLineItems" xlink:to="DerivativeLiabilityFairValueGrossAsset" xlink:title="definition: DerivativeLineItems to DerivativeLiabilityFairValueGrossAsset" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability" xlink:label="DerivativeFairValueOfDerivativeLiability" xlink:title="DerivativeFairValueOfDerivativeLiability" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DerivativeLineItems" xlink:to="DerivativeFairValueOfDerivativeLiability" xlink:title="definition: DerivativeLineItems to DerivativeFairValueOfDerivativeLiability" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeTable" xlink:label="DerivativeTable" xlink:title="DerivativeTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="DerivativeLineItems" xlink:to="DerivativeTable" xlink:title="definition: DerivativeLineItems to DerivativeTable" order="8.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="DerivativeInstrumentRiskAxis" xlink:title="DerivativeInstrumentRiskAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DerivativeTable" xlink:to="DerivativeInstrumentRiskAxis" xlink:title="definition: DerivativeTable to DerivativeInstrumentRiskAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="DerivativeContractTypeDomain" xlink:title="DerivativeContractTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="DerivativeInstrumentRiskAxis" xlink:to="DerivativeContractTypeDomain" xlink:title="definition: DerivativeInstrumentRiskAxis to DerivativeContractTypeDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="DerivativeContractTypeDomain_2" xlink:title="DerivativeContractTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="DerivativeInstrumentRiskAxis" xlink:to="DerivativeContractTypeDomain_2" xlink:title="definition: DerivativeInstrumentRiskAxis to DerivativeContractTypeDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_InterestRateSwapMember" xlink:label="InterestRateSwapMember" xlink:title="InterestRateSwapMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DerivativeContractTypeDomain" xlink:to="InterestRateSwapMember" xlink:title="definition: DerivativeContractTypeDomain to InterestRateSwapMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_HedgingDesignationAxis" xlink:label="HedgingDesignationAxis" xlink:title="HedgingDesignationAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DerivativeTable" xlink:to="HedgingDesignationAxis" xlink:title="definition: DerivativeTable to HedgingDesignationAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_HedgingDesignationDomain" xlink:label="HedgingDesignationDomain" xlink:title="HedgingDesignationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="HedgingDesignationAxis" xlink:to="HedgingDesignationDomain" xlink:title="definition: HedgingDesignationAxis to HedgingDesignationDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_HedgingDesignationDomain" xlink:label="HedgingDesignationDomain_2" xlink:title="HedgingDesignationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="HedgingDesignationAxis" xlink:to="HedgingDesignationDomain_2" xlink:title="definition: HedgingDesignationAxis to HedgingDesignationDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DesignatedAsHedgingInstrumentMember" xlink:label="DesignatedAsHedgingInstrumentMember" xlink:title="DesignatedAsHedgingInstrumentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="HedgingDesignationDomain" xlink:to="DesignatedAsHedgingInstrumentMember" xlink:title="definition: HedgingDesignationDomain to DesignatedAsHedgingInstrumentMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:label="DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:title="DerivativeInstrumentsGainLossByHedgingRelationshipAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DerivativeTable" xlink:to="DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:title="definition: DerivativeTable to DerivativeInstrumentsGainLossByHedgingRelationshipAxis" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="HedgingRelationshipDomain" xlink:title="HedgingRelationshipDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:to="HedgingRelationshipDomain" xlink:title="definition: DerivativeInstrumentsGainLossByHedgingRelationshipAxis to HedgingRelationshipDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="HedgingRelationshipDomain_2" xlink:title="HedgingRelationshipDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:to="HedgingRelationshipDomain_2" xlink:title="definition: DerivativeInstrumentsGainLossByHedgingRelationshipAxis to HedgingRelationshipDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_FairValueHedgingMember" xlink:label="FairValueHedgingMember" xlink:title="FairValueHedgingMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="HedgingRelationshipDomain" xlink:to="FairValueHedgingMember" xlink:title="definition: HedgingRelationshipDomain to FairValueHedgingMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="BalanceSheetLocationAxis" xlink:title="BalanceSheetLocationAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DerivativeTable" xlink:to="BalanceSheetLocationAxis" xlink:title="definition: DerivativeTable to BalanceSheetLocationAxis" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="BalanceSheetLocationDomain" xlink:title="BalanceSheetLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="BalanceSheetLocationAxis" xlink:to="BalanceSheetLocationDomain" xlink:title="definition: BalanceSheetLocationAxis to BalanceSheetLocationDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="BalanceSheetLocationDomain_2" xlink:title="BalanceSheetLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BalanceSheetLocationAxis" xlink:to="BalanceSheetLocationDomain_2" xlink:title="definition: BalanceSheetLocationAxis to BalanceSheetLocationDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherAssetsMember" xlink:label="OtherAssetsMember" xlink:title="OtherAssetsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BalanceSheetLocationDomain" xlink:to="OtherAssetsMember" xlink:title="definition: BalanceSheetLocationDomain to OtherAssetsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherLiabilitiesMember" xlink:label="OtherLiabilitiesMember" xlink:title="OtherLiabilitiesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="BalanceSheetLocationDomain" xlink:to="OtherLiabilitiesMember" xlink:title="definition: BalanceSheetLocationDomain to OtherLiabilitiesMember" order="2.0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://communitybankna.com/role/SegmentInformationDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="SegmentReportingInformationLineItems" xlink:title="SegmentReportingInformationLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SegmentReportingInformationAdditionalInformationAbstract" xlink:label="SegmentReportingInformationAdditionalInformationAbstract" xlink:title="SegmentReportingInformationAdditionalInformationAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingInformationLineItems" xlink:to="SegmentReportingInformationAdditionalInformationAbstract" xlink:title="definition: SegmentReportingInformationLineItems to SegmentReportingInformationAdditionalInformationAbstract" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_InterestIncomeExpenseNet" xlink:label="InterestIncomeExpenseNet" xlink:title="InterestIncomeExpenseNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingInformationLineItems" xlink:to="InterestIncomeExpenseNet" xlink:title="definition: SegmentReportingInformationLineItems to InterestIncomeExpenseNet" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ProvisionForLoanAndLeaseLosses" xlink:label="ProvisionForLoanAndLeaseLosses" xlink:title="ProvisionForLoanAndLeaseLosses" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingInformationLineItems" xlink:to="ProvisionForLoanAndLeaseLosses" xlink:title="definition: SegmentReportingInformationLineItems to ProvisionForLoanAndLeaseLosses" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_NoninterestIncome" xlink:label="NoninterestIncome" xlink:title="NoninterestIncome" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingInformationLineItems" xlink:to="NoninterestIncome" xlink:title="definition: SegmentReportingInformationLineItems to NoninterestIncome" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="AmortizationOfIntangibleAssets" xlink:title="AmortizationOfIntangibleAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingInformationLineItems" xlink:to="AmortizationOfIntangibleAssets" xlink:title="definition: SegmentReportingInformationLineItems to AmortizationOfIntangibleAssets" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts" xlink:label="BusinessCombinationAcquisitionRelatedCosts" xlink:title="BusinessCombinationAcquisitionRelatedCosts" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingInformationLineItems" xlink:to="BusinessCombinationAcquisitionRelatedCosts" xlink:title="definition: SegmentReportingInformationLineItems to BusinessCombinationAcquisitionRelatedCosts" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OtherCostAndExpenseOperating" xlink:label="OtherCostAndExpenseOperating" xlink:title="OtherCostAndExpenseOperating" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingInformationLineItems" xlink:to="OtherCostAndExpenseOperating" xlink:title="definition: SegmentReportingInformationLineItems to OtherCostAndExpenseOperating" order="7.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:label="IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:title="IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingInformationLineItems" xlink:to="IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:title="definition: SegmentReportingInformationLineItems to IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" order="8.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_Assets" xlink:label="Assets" xlink:title="Assets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingInformationLineItems" xlink:to="Assets" xlink:title="definition: SegmentReportingInformationLineItems to Assets" order="9.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_Goodwill" xlink:label="Goodwill" xlink:title="Goodwill" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingInformationLineItems" xlink:to="Goodwill" xlink:title="definition: SegmentReportingInformationLineItems to Goodwill" order="10.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="ScheduleOfSegmentReportingInformationBySegmentTable" xlink:title="ScheduleOfSegmentReportingInformationBySegmentTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="SegmentReportingInformationLineItems" xlink:to="ScheduleOfSegmentReportingInformationBySegmentTable" xlink:title="definition: SegmentReportingInformationLineItems to ScheduleOfSegmentReportingInformationBySegmentTable" order="11.0" t1:closed="true" t1:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="StatementBusinessSegmentsAxis" xlink:title="StatementBusinessSegmentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="StatementBusinessSegmentsAxis" xlink:title="definition: ScheduleOfSegmentReportingInformationBySegmentTable to StatementBusinessSegmentsAxis" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SegmentDomain" xlink:label="SegmentDomain" xlink:title="SegmentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementBusinessSegmentsAxis" xlink:to="SegmentDomain" xlink:title="definition: StatementBusinessSegmentsAxis to SegmentDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_SegmentDomain" xlink:label="SegmentDomain_2" xlink:title="SegmentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementBusinessSegmentsAxis" xlink:to="SegmentDomain_2" xlink:title="definition: StatementBusinessSegmentsAxis to SegmentDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_BankingMember" xlink:label="BankingMember" xlink:title="BankingMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentDomain" xlink:to="BankingMember" xlink:title="definition: SegmentDomain to BankingMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="cbu-20180630.xsd#cbu_EmployeeBenefitServicesMember" xlink:label="EmployeeBenefitServicesMember" xlink:title="EmployeeBenefitServicesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentDomain" xlink:to="EmployeeBenefitServicesMember" xlink:title="definition: SegmentDomain to EmployeeBenefitServicesMember" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_AllOtherSegmentsMember" xlink:label="AllOtherSegmentsMember" xlink:title="AllOtherSegmentsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentDomain" xlink:to="AllOtherSegmentsMember" xlink:title="definition: SegmentDomain to AllOtherSegmentsMember" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_ConsolidationItemsAxis" xlink:label="ConsolidationItemsAxis" xlink:title="ConsolidationItemsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="ConsolidationItemsAxis" xlink:title="definition: ScheduleOfSegmentReportingInformationBySegmentTable to ConsolidationItemsAxis" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_ConsolidationItemsDomain" xlink:label="ConsolidationItemsDomain" xlink:title="ConsolidationItemsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ConsolidationItemsAxis" xlink:to="ConsolidationItemsDomain" xlink:title="definition: ConsolidationItemsAxis to ConsolidationItemsDomain" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd#srt_ConsolidationItemsDomain" xlink:label="ConsolidationItemsDomain_2" xlink:title="ConsolidationItemsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ConsolidationItemsAxis" xlink:to="ConsolidationItemsDomain_2" xlink:title="definition: ConsolidationItemsAxis to ConsolidationItemsDomain_2" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_OperatingSegmentsMember" xlink:label="OperatingSegmentsMember" xlink:title="OperatingSegmentsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidationItemsDomain" xlink:to="OperatingSegmentsMember" xlink:title="definition: ConsolidationItemsDomain to OperatingSegmentsMember" order="1.0" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd#us-gaap_IntersegmentEliminationMember" xlink:label="IntersegmentEliminationMember" xlink:title="IntersegmentEliminationMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidationItemsDomain" xlink:to="IntersegmentEliminationMember" xlink:title="definition: ConsolidationItemsDomain to IntersegmentEliminationMember" order="2.0" />
  </link:definitionLink>
</link:linkbase>
