<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2022 Workiva-->
<!--r:af7430aa-3668-4890-81e7-f59199209d00,g:0ec205f8-1d5e-41d6-b9cb-c8e004e72634-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <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: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:roleRef roleURI="http://www.ies-co.com/role/DEIDocument" xlink:type="simple" xlink:href="iesc-20211231.xsd#DEIDocument"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/DEIDocument" xlink:type="extended" id="ia98444a278ca4347b4af4eb03546b9dc_DEIDocument">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_a6eaa46c-8542-473b-9c89-a50717a59163" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityFileNumber_a6eaa46c-8542-473b-9c89-a50717a59163" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_8ffaf82d-c10d-4ba8-b70a-74a0d31d9154" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityRegistrantName_8ffaf82d-c10d-4ba8-b70a-74a0d31d9154" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_20d764a0-a355-4ba0-a2d9-7fedad364efd" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_DocumentPeriodEndDate_20d764a0-a355-4ba0-a2d9-7fedad364efd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_47e49bcf-1662-4f43-bbef-a96604faf9b6" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_DocumentQuarterlyReport_47e49bcf-1662-4f43-bbef-a96604faf9b6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_4a249374-864a-4f75-81eb-d028f39541d4" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_DocumentTransitionReport_4a249374-864a-4f75-81eb-d028f39541d4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_2cbacf75-b251-4d37-9bf3-dd1f40c6cfab" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityCentralIndexKey_2cbacf75-b251-4d37-9bf3-dd1f40c6cfab" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_8624ca4e-6b80-4d17-82a6-fb575cab45c1" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityIncorporationStateCountryCode_8624ca4e-6b80-4d17-82a6-fb575cab45c1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_9002014c-0c97-404c-8540-43482fbb781c" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_DocumentType_9002014c-0c97-404c-8540-43482fbb781c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_9c80e284-dae7-4d62-b9ac-0e8ee54a5aed" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_AmendmentFlag_9c80e284-dae7-4d62-b9ac-0e8ee54a5aed" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_d72f639a-44ac-404e-8ccd-a1f7b32a53fc" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_DocumentFiscalYearFocus_d72f639a-44ac-404e-8ccd-a1f7b32a53fc" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_bbafc9aa-0af1-4d3c-89fc-6ffc2d551960" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_DocumentFiscalPeriodFocus_bbafc9aa-0af1-4d3c-89fc-6ffc2d551960" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_d473d31b-5ae5-4d51-a18f-ac7fc65b82f5" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_CurrentFiscalYearEndDate_d473d31b-5ae5-4d51-a18f-ac7fc65b82f5" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_8fd4d236-9291-498c-9c48-0a7ebb2a4c0b" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityFilerCategory_8fd4d236-9291-498c-9c48-0a7ebb2a4c0b" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_02636070-1ca0-4369-9bc1-34d968254a71" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityTaxIdentificationNumber_02636070-1ca0-4369-9bc1-34d968254a71" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_c0cfbafe-b905-4e40-a52c-78231ab7d5aa" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_Security12bTitle_c0cfbafe-b905-4e40-a52c-78231ab7d5aa" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_97724c31-9922-4621-810f-c7a5e0b1da09" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_TradingSymbol_97724c31-9922-4621-810f-c7a5e0b1da09" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_d05c1591-2391-4889-a079-0042e8b51fb7" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_SecurityExchangeName_d05c1591-2391-4889-a079-0042e8b51fb7" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_af8ff686-e2b8-4141-bab0-3499328a2093" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityCurrentReportingStatus_af8ff686-e2b8-4141-bab0-3499328a2093" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_b5f4ffb3-4753-41bb-8409-d645e4c26e65" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityInteractiveDataCurrent_b5f4ffb3-4753-41bb-8409-d645e4c26e65" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_57f579a4-e3ff-456b-b585-bea15500ffdb" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityShellCompany_57f579a4-e3ff-456b-b585-bea15500ffdb" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_b6c53038-9be2-48a2-b69e-7ad4b5f06a9d" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntitySmallBusiness_b6c53038-9be2-48a2-b69e-7ad4b5f06a9d" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_9e22fc24-864a-4922-8e50-7335340613f1" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityEmergingGrowthCompany_9e22fc24-864a-4922-8e50-7335340613f1" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_d9a73619-0520-49f7-a5f9-57786bfa273d" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityAddressAddressLine1_d9a73619-0520-49f7-a5f9-57786bfa273d" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_a8ddf010-45de-49ae-928d-626939b69adc" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityAddressAddressLine2_a8ddf010-45de-49ae-928d-626939b69adc" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_075dcb80-f29b-4fed-b98c-832ad39894a3" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityAddressCityOrTown_075dcb80-f29b-4fed-b98c-832ad39894a3" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_9b791c54-f773-447f-b15a-184725fae919" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityAddressStateOrProvince_9b791c54-f773-447f-b15a-184725fae919" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_41564a4c-7ab3-49a2-8323-9534d6eab0a4" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityAddressPostalZipCode_41564a4c-7ab3-49a2-8323-9534d6eab0a4" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_b45957fa-8279-4d63-b5dd-2f80968cb235" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_CityAreaCode_b45957fa-8279-4d63-b5dd-2f80968cb235" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_536ee7de-7566-4020-b47e-c587850da44f" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_LocalPhoneNumber_536ee7de-7566-4020-b47e-c587850da44f" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_f4497611-4488-4a58-a8d5-d5fec6057c76" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_f4497611-4488-4a58-a8d5-d5fec6057c76" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_cd5f54e1-1d7c-4770-8c9c-217447be39b5" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_38a73f88-2042-467e-8214-47011d2e7011" xlink:to="loc_dei_EntitiesTable_cd5f54e1-1d7c-4770-8c9c-217447be39b5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_97b1926b-a770-41ad-9555-96d1d918c445" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_cd5f54e1-1d7c-4770-8c9c-217447be39b5" xlink:to="loc_us-gaap_StatementClassOfStockAxis_97b1926b-a770-41ad-9555-96d1d918c445" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_97b1926b-a770-41ad-9555-96d1d918c445_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_97b1926b-a770-41ad-9555-96d1d918c445" xlink:to="loc_us-gaap_ClassOfStockDomain_97b1926b-a770-41ad-9555-96d1d918c445_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_40ce69e0-fac9-43d3-9aba-d35756612b66" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_97b1926b-a770-41ad-9555-96d1d918c445" xlink:to="loc_us-gaap_ClassOfStockDomain_40ce69e0-fac9-43d3-9aba-d35756612b66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_cfc99876-4657-457c-b989-4646df570ca6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_40ce69e0-fac9-43d3-9aba-d35756612b66" xlink:to="loc_us-gaap_CommonStockMember_cfc99876-4657-457c-b989-4646df570ca6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/ConsolidatedStatementsofStockholdersEquity" xlink:type="simple" xlink:href="iesc-20211231.xsd#ConsolidatedStatementsofStockholdersEquity"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/ConsolidatedStatementsofStockholdersEquity" xlink:type="extended" id="i2762aa9f86ee4ee09fcac802950c41fb_ConsolidatedStatementsofStockholdersEquity">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_4637cba7-9cc1-4c10-9d2b-4b921b9de309" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_b2766355-8644-418b-bda1-78f6f666781f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_4637cba7-9cc1-4c10-9d2b-4b921b9de309" xlink:to="loc_us-gaap_StockholdersEquity_b2766355-8644-418b-bda1-78f6f666781f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_cc02c427-0fe5-45d0-ab5d-6a2267863e3b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_4637cba7-9cc1-4c10-9d2b-4b921b9de309" xlink:to="loc_us-gaap_SharesIssued_cc02c427-0fe5-45d0-ab5d-6a2267863e3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_f13eebf9-e028-40cf-b236-a1bbb5e9a8ff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_4637cba7-9cc1-4c10-9d2b-4b921b9de309" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_f13eebf9-e028-40cf-b236-a1bbb5e9a8ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_8f06ac87-e866-4217-a372-1d23d46f1100" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_4637cba7-9cc1-4c10-9d2b-4b921b9de309" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_8f06ac87-e866-4217-a372-1d23d46f1100" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_ffb669f0-0a2f-496e-957f-561acdeeff42" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_4637cba7-9cc1-4c10-9d2b-4b921b9de309" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_ffb669f0-0a2f-496e-957f-561acdeeff42" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_f30df130-a46e-493d-aa7b-9be8915181c6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_4637cba7-9cc1-4c10-9d2b-4b921b9de309" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_f30df130-a46e-493d-aa7b-9be8915181c6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_a8b69a06-7846-4deb-8810-33a88573ac5a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_4637cba7-9cc1-4c10-9d2b-4b921b9de309" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_a8b69a06-7846-4deb-8810-33a88573ac5a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestChangeInRedemptionValue_8f09ce81-d8f8-4fd4-bc20-7f47c8d2ae1b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MinorityInterestChangeInRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_4637cba7-9cc1-4c10-9d2b-4b921b9de309" xlink:to="loc_us-gaap_MinorityInterestChangeInRedemptionValue_8f09ce81-d8f8-4fd4-bc20-7f47c8d2ae1b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_7b23ab3b-90f3-4f5d-b0e7-67e7e5618be0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_4637cba7-9cc1-4c10-9d2b-4b921b9de309" xlink:to="loc_us-gaap_NetIncomeLoss_7b23ab3b-90f3-4f5d-b0e7-67e7e5618be0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_abd1b85f-8167-4ff6-ac4a-1cbb69c9d031" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_a10ac690-9e18-45d6-a247-d7206f37d015" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_259d8107-b150-4729-a7df-6a8d62d0c4f0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_4637cba7-9cc1-4c10-9d2b-4b921b9de309" xlink:to="loc_us-gaap_StatementTable_259d8107-b150-4729-a7df-6a8d62d0c4f0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_c48069ab-e281-41d6-a789-f11027b95530" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_259d8107-b150-4729-a7df-6a8d62d0c4f0" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_c48069ab-e281-41d6-a789-f11027b95530" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_c48069ab-e281-41d6-a789-f11027b95530_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_c48069ab-e281-41d6-a789-f11027b95530" xlink:to="loc_us-gaap_EquityComponentDomain_c48069ab-e281-41d6-a789-f11027b95530_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_60d78479-1553-4b8c-9b73-5d81735cff3a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_c48069ab-e281-41d6-a789-f11027b95530" xlink:to="loc_us-gaap_EquityComponentDomain_60d78479-1553-4b8c-9b73-5d81735cff3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_448b7dd3-7439-4e2c-bec5-a13c24c86f6a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_60d78479-1553-4b8c-9b73-5d81735cff3a" xlink:to="loc_us-gaap_CommonStockMember_448b7dd3-7439-4e2c-bec5-a13c24c86f6a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockMember_df29ff56-d24a-4bba-add1-dc89969d4e1a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_60d78479-1553-4b8c-9b73-5d81735cff3a" xlink:to="loc_us-gaap_TreasuryStockMember_df29ff56-d24a-4bba-add1-dc89969d4e1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_c57b807f-a07e-4053-ba7e-466ab9193b2e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_60d78479-1553-4b8c-9b73-5d81735cff3a" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_c57b807f-a07e-4053-ba7e-466ab9193b2e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_571c3388-d0f1-4f0f-9b6f-31b7cc1b6d87" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_60d78479-1553-4b8c-9b73-5d81735cff3a" xlink:to="loc_us-gaap_RetainedEarningsMember_571c3388-d0f1-4f0f-9b6f-31b7cc1b6d87" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_ae210e42-969e-41f2-b1a2-f36228512ffb" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_259d8107-b150-4729-a7df-6a8d62d0c4f0" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_ae210e42-969e-41f2-b1a2-f36228512ffb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_ae210e42-969e-41f2-b1a2-f36228512ffb_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_ae210e42-969e-41f2-b1a2-f36228512ffb" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_ae210e42-969e-41f2-b1a2-f36228512ffb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_c6192e7c-f210-4b9c-8d3c-a99086a61d20" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_ae210e42-969e-41f2-b1a2-f36228512ffb" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_c6192e7c-f210-4b9c-8d3c-a99086a61d20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_76d088c7-5572-4044-8cc3-8d736ceb3f2b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_c6192e7c-f210-4b9c-8d3c-a99086a61d20" xlink:to="loc_us-gaap_RetainedEarningsMember_76d088c7-5572-4044-8cc3-8d736ceb3f2b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_9f102039-593c-4da4-9e59-53215f3396f0" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_c6192e7c-f210-4b9c-8d3c-a99086a61d20" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_9f102039-593c-4da4-9e59-53215f3396f0" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/RevenueRecognitionDetails" xlink:type="simple" xlink:href="iesc-20211231.xsd#RevenueRecognitionDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/RevenueRecognitionDetails" xlink:type="extended" id="iae999dd2e45141e0867594b703c632ad_RevenueRecognitionDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_67396f13-d491-4547-b679-b771cbabbd09" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_2a78ef50-3aac-4d49-b0b6-04ab15d26f72" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_67396f13-d491-4547-b679-b771cbabbd09" xlink:to="loc_us-gaap_Revenues_2a78ef50-3aac-4d49-b0b6-04ab15d26f72" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_007d94dd-490a-4f8e-ba38-80a3cf7ec4f2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_67396f13-d491-4547-b679-b771cbabbd09" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_007d94dd-490a-4f8e-ba38-80a3cf7ec4f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_7f0e1873-2ea8-40d9-b194-a87a96a11b99" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_67396f13-d491-4547-b679-b771cbabbd09" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_7f0e1873-2ea8-40d9-b194-a87a96a11b99" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_c627fc77-4ea9-4ab4-a905-9d72d3ffb24c" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_7f0e1873-2ea8-40d9-b194-a87a96a11b99" xlink:to="loc_srt_ProductOrServiceAxis_c627fc77-4ea9-4ab4-a905-9d72d3ffb24c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_c627fc77-4ea9-4ab4-a905-9d72d3ffb24c_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_c627fc77-4ea9-4ab4-a905-9d72d3ffb24c" xlink:to="loc_srt_ProductsAndServicesDomain_c627fc77-4ea9-4ab4-a905-9d72d3ffb24c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_5e417e1b-dd38-44bb-a6e8-56d99f0fa2cf" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_c627fc77-4ea9-4ab4-a905-9d72d3ffb24c" xlink:to="loc_srt_ProductsAndServicesDomain_5e417e1b-dd38-44bb-a6e8-56d99f0fa2cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_IndustrialServicesMember_e52dcc11-5239-4988-b3a5-150c5758939a" xlink:href="iesc-20211231.xsd#iesc_IndustrialServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_5e417e1b-dd38-44bb-a6e8-56d99f0fa2cf" xlink:to="loc_iesc_IndustrialServicesMember_e52dcc11-5239-4988-b3a5-150c5758939a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_CustomPowerSolutionsMember_c0bfe89f-feb2-4e3a-8c97-520f281427e9" xlink:href="iesc-20211231.xsd#iesc_CustomPowerSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_5e417e1b-dd38-44bb-a6e8-56d99f0fa2cf" xlink:to="loc_iesc_CustomPowerSolutionsMember_c0bfe89f-feb2-4e3a-8c97-520f281427e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_SingleFamilyContractsMember_9ea24182-8cb1-4329-b178-9b07a9f61472" xlink:href="iesc-20211231.xsd#iesc_SingleFamilyContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_5e417e1b-dd38-44bb-a6e8-56d99f0fa2cf" xlink:to="loc_iesc_SingleFamilyContractsMember_9ea24182-8cb1-4329-b178-9b07a9f61472" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_MultiFamilyandOtherMember_c00bf4fc-7dfc-47fa-a360-0917ed4006bd" xlink:href="iesc-20211231.xsd#iesc_MultiFamilyandOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_5e417e1b-dd38-44bb-a6e8-56d99f0fa2cf" xlink:to="loc_iesc_MultiFamilyandOtherMember_c00bf4fc-7dfc-47fa-a360-0917ed4006bd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_7be709be-073b-41f2-971c-93da9688aad6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerBasisOfPricingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_7f0e1873-2ea8-40d9-b194-a87a96a11b99" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_7be709be-073b-41f2-971c-93da9688aad6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_7be709be-073b-41f2-971c-93da9688aad6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerBasisOfPricingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_7be709be-073b-41f2-971c-93da9688aad6" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_7be709be-073b-41f2-971c-93da9688aad6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_eb9f33c2-dbea-4843-89e6-4bc1702c1fcd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerBasisOfPricingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_7be709be-073b-41f2-971c-93da9688aad6" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_eb9f33c2-dbea-4843-89e6-4bc1702c1fcd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedPriceContractMember_344fb90b-8a37-4af4-9976-c5a1eb7dbb88" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FixedPriceContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_eb9f33c2-dbea-4843-89e6-4bc1702c1fcd" xlink:to="loc_us-gaap_FixedPriceContractMember_344fb90b-8a37-4af4-9976-c5a1eb7dbb88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimeAndMaterialsContractMember_22f07cd4-fc46-4dc3-beb0-b54bd19404f3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TimeAndMaterialsContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_eb9f33c2-dbea-4843-89e6-4bc1702c1fcd" xlink:to="loc_us-gaap_TimeAndMaterialsContractMember_22f07cd4-fc46-4dc3-beb0-b54bd19404f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_9982e0c5-6aac-42c6-9f1c-a02dd51561d3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_7f0e1873-2ea8-40d9-b194-a87a96a11b99" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_9982e0c5-6aac-42c6-9f1c-a02dd51561d3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_9982e0c5-6aac-42c6-9f1c-a02dd51561d3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_9982e0c5-6aac-42c6-9f1c-a02dd51561d3" xlink:to="loc_us-gaap_SegmentDomain_9982e0c5-6aac-42c6-9f1c-a02dd51561d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_dfddd5cb-9044-43c1-aece-fb57bd3d02a6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_9982e0c5-6aac-42c6-9f1c-a02dd51561d3" xlink:to="loc_us-gaap_SegmentDomain_dfddd5cb-9044-43c1-aece-fb57bd3d02a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_CommercialandIndustrialMember_fcc43833-824d-422f-98e7-c9a7581a7acf" xlink:href="iesc-20211231.xsd#iesc_CommercialandIndustrialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_dfddd5cb-9044-43c1-aece-fb57bd3d02a6" xlink:to="loc_iesc_CommercialandIndustrialMember_fcc43833-824d-422f-98e7-c9a7581a7acf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_CommunicationsMember_b68ff5f6-22f4-4206-8885-4fc3d1fb3c44" xlink:href="iesc-20211231.xsd#iesc_CommunicationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_dfddd5cb-9044-43c1-aece-fb57bd3d02a6" xlink:to="loc_iesc_CommunicationsMember_b68ff5f6-22f4-4206-8885-4fc3d1fb3c44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_InfrastructureSolutionsMember_3c62b829-79cf-4af1-ba88-171ee066b4b8" xlink:href="iesc-20211231.xsd#iesc_InfrastructureSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_dfddd5cb-9044-43c1-aece-fb57bd3d02a6" xlink:to="loc_iesc_InfrastructureSolutionsMember_3c62b829-79cf-4af1-ba88-171ee066b4b8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_ResidentialMember_c56be5c7-a278-489f-bf65-6772bf6ab635" xlink:href="iesc-20211231.xsd#iesc_ResidentialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_dfddd5cb-9044-43c1-aece-fb57bd3d02a6" xlink:to="loc_iesc_ResidentialMember_c56be5c7-a278-489f-bf65-6772bf6ab635" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/OperatingSegmentsDetails" xlink:type="simple" xlink:href="iesc-20211231.xsd#OperatingSegmentsDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/OperatingSegmentsDetails" xlink:type="extended" id="i67aab84694e94237b1cc390efda04306_OperatingSegmentsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_18619dbf-093a-42c1-86ec-255503a557a7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_86cf3e9f-62cf-4e92-aa2a-e94e0d1f3c6a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_18619dbf-093a-42c1-86ec-255503a557a7" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_86cf3e9f-62cf-4e92-aa2a-e94e0d1f3c6a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_ef9378f0-f36e-4b0b-816f-b8c0284646f9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_18619dbf-093a-42c1-86ec-255503a557a7" xlink:to="loc_us-gaap_GrossProfit_ef9378f0-f36e-4b0b-816f-b8c0284646f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_34b995f3-deee-43e4-a5a5-7f6a58075cb6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_18619dbf-093a-42c1-86ec-255503a557a7" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_34b995f3-deee-43e4-a5a5-7f6a58075cb6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationIntegrationRelatedCosts_8b037e1d-9e11-4ffb-a477-48e4b100439f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationIntegrationRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_18619dbf-093a-42c1-86ec-255503a557a7" xlink:to="loc_us-gaap_BusinessCombinationIntegrationRelatedCosts_8b037e1d-9e11-4ffb-a477-48e4b100439f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDispositionOfAssets1_991b3cf1-8bc8-44d9-8374-d6ebf0412ef7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GainLossOnDispositionOfAssets1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_18619dbf-093a-42c1-86ec-255503a557a7" xlink:to="loc_us-gaap_GainLossOnDispositionOfAssets1_991b3cf1-8bc8-44d9-8374-d6ebf0412ef7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_843842d2-7680-4500-a00e-8bf7a6f2003b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_18619dbf-093a-42c1-86ec-255503a557a7" xlink:to="loc_us-gaap_OperatingIncomeLoss_843842d2-7680-4500-a00e-8bf7a6f2003b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_263f1876-9f48-443f-82cc-26fd658540c0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_18619dbf-093a-42c1-86ec-255503a557a7" xlink:to="loc_us-gaap_Depreciation_263f1876-9f48-443f-82cc-26fd658540c0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireProductiveAssets_dbabecb9-d9f4-4cc6-9e5f-c989c9658b85" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsToAcquireProductiveAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_18619dbf-093a-42c1-86ec-255503a557a7" xlink:to="loc_us-gaap_PaymentsToAcquireProductiveAssets_dbabecb9-d9f4-4cc6-9e5f-c989c9658b85" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_e031ae07-f4bb-41a4-a547-87a70b789f2f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_18619dbf-093a-42c1-86ec-255503a557a7" xlink:to="loc_us-gaap_Assets_e031ae07-f4bb-41a4-a547-87a70b789f2f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_fa3db2d7-1fd1-442f-8d98-57aba73c113a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_18619dbf-093a-42c1-86ec-255503a557a7" xlink:to="loc_us-gaap_Revenues_fa3db2d7-1fd1-442f-8d98-57aba73c113a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_add78966-7ff8-446b-a9f7-20236c3fdf06" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_18619dbf-093a-42c1-86ec-255503a557a7" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_add78966-7ff8-446b-a9f7-20236c3fdf06" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_9447b4ba-b021-4421-bcfa-121957315c6d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_add78966-7ff8-446b-a9f7-20236c3fdf06" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_9447b4ba-b021-4421-bcfa-121957315c6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_9447b4ba-b021-4421-bcfa-121957315c6d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_9447b4ba-b021-4421-bcfa-121957315c6d" xlink:to="loc_us-gaap_SegmentDomain_9447b4ba-b021-4421-bcfa-121957315c6d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_73cf805a-0b19-4dce-b8e4-724b9455fe1e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_9447b4ba-b021-4421-bcfa-121957315c6d" xlink:to="loc_us-gaap_SegmentDomain_73cf805a-0b19-4dce-b8e4-724b9455fe1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_CommercialandIndustrialMember_34c326c7-0d75-4205-a9a4-1304dbeb0b5d" xlink:href="iesc-20211231.xsd#iesc_CommercialandIndustrialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_73cf805a-0b19-4dce-b8e4-724b9455fe1e" xlink:to="loc_iesc_CommercialandIndustrialMember_34c326c7-0d75-4205-a9a4-1304dbeb0b5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_CommunicationsMember_3fd7b08a-8baa-4800-8cc6-641e1256b73c" xlink:href="iesc-20211231.xsd#iesc_CommunicationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_73cf805a-0b19-4dce-b8e4-724b9455fe1e" xlink:to="loc_iesc_CommunicationsMember_3fd7b08a-8baa-4800-8cc6-641e1256b73c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_InfrastructureSolutionsMember_5ee91f49-a30e-414b-b114-c8408c20284a" xlink:href="iesc-20211231.xsd#iesc_InfrastructureSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_73cf805a-0b19-4dce-b8e4-724b9455fe1e" xlink:to="loc_iesc_InfrastructureSolutionsMember_5ee91f49-a30e-414b-b114-c8408c20284a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_ResidentialMember_13c2ef69-42f4-4ab6-b8ff-0842495dd73e" xlink:href="iesc-20211231.xsd#iesc_ResidentialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_73cf805a-0b19-4dce-b8e4-724b9455fe1e" xlink:to="loc_iesc_ResidentialMember_13c2ef69-42f4-4ab6-b8ff-0842495dd73e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateMember_e1ecbd97-b1ed-4030-b906-7c57cf2f3c92" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CorporateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_73cf805a-0b19-4dce-b8e4-724b9455fe1e" xlink:to="loc_us-gaap_CorporateMember_e1ecbd97-b1ed-4030-b906-7c57cf2f3c92" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/StockholdersEquityDetails" xlink:type="simple" xlink:href="iesc-20211231.xsd#StockholdersEquityDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/StockholdersEquityDetails" xlink:type="extended" id="i670ce02e15d94d12a0f05960800e4b36_StockholdersEquityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94f8334d-14ef-4073-999b-58ab234b56c7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_ef64c8bb-8976-461e-af9f-a30e74b1793b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94f8334d-14ef-4073-999b-58ab234b56c7" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_ef64c8bb-8976-461e-af9f-a30e74b1793b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_61504201-6034-4603-8650-8e580014857f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94f8334d-14ef-4073-999b-58ab234b56c7" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_61504201-6034-4603-8650-8e580014857f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_b535bc57-3701-4a0f-98d3-fda8d1e94f57" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94f8334d-14ef-4073-999b-58ab234b56c7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_b535bc57-3701-4a0f-98d3-fda8d1e94f57" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_4ec4ad1c-51fd-45aa-ba2b-a5f5eede2aa9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94f8334d-14ef-4073-999b-58ab234b56c7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_4ec4ad1c-51fd-45aa-ba2b-a5f5eede2aa9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_f75e7d97-ed02-40d6-b931-833a1e2d3571" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94f8334d-14ef-4073-999b-58ab234b56c7" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_f75e7d97-ed02-40d6-b931-833a1e2d3571" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_4507e9b0-bf1b-4a9f-9267-d0f6bcddfb67" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94f8334d-14ef-4073-999b-58ab234b56c7" xlink:to="loc_us-gaap_SharesIssued_4507e9b0-bf1b-4a9f-9267-d0f6bcddfb67" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited_56215f8c-4cdc-4c7d-a113-67e3bf73d424" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94f8334d-14ef-4073-999b-58ab234b56c7" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited_56215f8c-4cdc-4c7d-a113-67e3bf73d424" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_Sharesvested_9da10788-6fb8-455d-aeeb-8359eae22dd1" xlink:href="iesc-20211231.xsd#iesc_Sharesvested"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94f8334d-14ef-4073-999b-58ab234b56c7" xlink:to="loc_iesc_Sharesvested_9da10788-6fb8-455d-aeeb-8359eae22dd1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_5faeac12-00e6-4d9c-99e9-b63115cfce22" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94f8334d-14ef-4073-999b-58ab234b56c7" xlink:to="loc_us-gaap_SharesOutstanding_5faeac12-00e6-4d9c-99e9-b63115cfce22" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockAcquiredAverageCostPerShare_c67fb814-4a9b-46d6-a8eb-7ed1700faf30" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockAcquiredAverageCostPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94f8334d-14ef-4073-999b-58ab234b56c7" xlink:to="loc_us-gaap_TreasuryStockAcquiredAverageCostPerShare_c67fb814-4a9b-46d6-a8eb-7ed1700faf30" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_95a6fbc7-42d9-4778-b0b4-1d82717328ad" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94f8334d-14ef-4073-999b-58ab234b56c7" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_95a6fbc7-42d9-4778-b0b4-1d82717328ad" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_72dd7735-9424-4964-aa95-134513e6b248" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94f8334d-14ef-4073-999b-58ab234b56c7" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_72dd7735-9424-4964-aa95-134513e6b248" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_ab96a169-5095-43b8-8639-a28ac53dc318" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_94f8334d-14ef-4073-999b-58ab234b56c7" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_ab96a169-5095-43b8-8639-a28ac53dc318" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareRepurchaseProgramAxis_b31308fe-337d-48b3-b18e-f51ab39e7a81" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_ab96a169-5095-43b8-8639-a28ac53dc318" xlink:to="loc_us-gaap_ShareRepurchaseProgramAxis_b31308fe-337d-48b3-b18e-f51ab39e7a81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareRepurchaseProgramDomain_b31308fe-337d-48b3-b18e-f51ab39e7a81_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShareRepurchaseProgramAxis_b31308fe-337d-48b3-b18e-f51ab39e7a81" xlink:to="loc_us-gaap_ShareRepurchaseProgramDomain_b31308fe-337d-48b3-b18e-f51ab39e7a81_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareRepurchaseProgramDomain_9d209caa-07ca-40e2-96b8-580f10ee39ed" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShareRepurchaseProgramAxis_b31308fe-337d-48b3-b18e-f51ab39e7a81" xlink:to="loc_us-gaap_ShareRepurchaseProgramDomain_9d209caa-07ca-40e2-96b8-580f10ee39ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_EquityIncentivePlanMember_ca9fdf33-cf61-4163-9bc5-29e5b6815584" xlink:href="iesc-20211231.xsd#iesc_EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareRepurchaseProgramDomain_9d209caa-07ca-40e2-96b8-580f10ee39ed" xlink:to="loc_iesc_EquityIncentivePlanMember_ca9fdf33-cf61-4163-9bc5-29e5b6815584" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepurchaseAgreementsMember_4b0a435c-5dbb-4d1d-8b49-b10fbbc7b94f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RepurchaseAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareRepurchaseProgramDomain_9d209caa-07ca-40e2-96b8-580f10ee39ed" xlink:to="loc_us-gaap_RepurchaseAgreementsMember_4b0a435c-5dbb-4d1d-8b49-b10fbbc7b94f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusAxis_ae83e05f-f10e-4210-be98-5eb91549ca99" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GranteeStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_ab96a169-5095-43b8-8639-a28ac53dc318" xlink:to="loc_us-gaap_GranteeStatusAxis_ae83e05f-f10e-4210-be98-5eb91549ca99" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_ae83e05f-f10e-4210-be98-5eb91549ca99_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GranteeStatusAxis_ae83e05f-f10e-4210-be98-5eb91549ca99" xlink:to="loc_us-gaap_GranteeStatusDomain_ae83e05f-f10e-4210-be98-5eb91549ca99_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_af106971-1d03-4394-b9a1-39f46355afce" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GranteeStatusAxis_ae83e05f-f10e-4210-be98-5eb91549ca99" xlink:to="loc_us-gaap_GranteeStatusDomain_af106971-1d03-4394-b9a1-39f46355afce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_0f060513-d758-4b58-a2eb-207acb547526" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedPaymentArrangementNonemployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_af106971-1d03-4394-b9a1-39f46355afce" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_0f060513-d758-4b58-a2eb-207acb547526" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_fb3031ee-990a-44ed-8149-7d67942d089b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedPaymentArrangementEmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_af106971-1d03-4394-b9a1-39f46355afce" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_fb3031ee-990a-44ed-8149-7d67942d089b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_ff952ff5-a2f9-4aea-88b7-ccc759b5372f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_ab96a169-5095-43b8-8639-a28ac53dc318" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_ff952ff5-a2f9-4aea-88b7-ccc759b5372f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_ff952ff5-a2f9-4aea-88b7-ccc759b5372f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_ff952ff5-a2f9-4aea-88b7-ccc759b5372f" xlink:to="loc_us-gaap_EquityComponentDomain_ff952ff5-a2f9-4aea-88b7-ccc759b5372f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_2b6de8db-b682-401f-863e-c6fe9ce23691" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_ff952ff5-a2f9-4aea-88b7-ccc759b5372f" xlink:to="loc_us-gaap_EquityComponentDomain_2b6de8db-b682-401f-863e-c6fe9ce23691" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockMember_574c7935-5f29-4d7d-b01c-7a315eb91cef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2b6de8db-b682-401f-863e-c6fe9ce23691" xlink:to="loc_us-gaap_TreasuryStockMember_574c7935-5f29-4d7d-b01c-7a315eb91cef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_50168812-91ea-4883-831b-bb8dc3788faa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_ab96a169-5095-43b8-8639-a28ac53dc318" xlink:to="loc_us-gaap_AwardTypeAxis_50168812-91ea-4883-831b-bb8dc3788faa" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_50168812-91ea-4883-831b-bb8dc3788faa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_50168812-91ea-4883-831b-bb8dc3788faa" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_50168812-91ea-4883-831b-bb8dc3788faa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7c5a7ae8-5cfe-465c-9318-3c8dab97bff3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_50168812-91ea-4883-831b-bb8dc3788faa" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7c5a7ae8-5cfe-465c-9318-3c8dab97bff3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_267bedc3-fa91-4982-abe9-5066bd80d8b5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7c5a7ae8-5cfe-465c-9318-3c8dab97bff3" xlink:to="loc_us-gaap_RestrictedStockMember_267bedc3-fa91-4982-abe9-5066bd80d8b5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PhantomShareUnitsPSUsMember_e666a3cc-0cae-43f5-9a0b-dbd25dcd0801" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PhantomShareUnitsPSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7c5a7ae8-5cfe-465c-9318-3c8dab97bff3" xlink:to="loc_us-gaap_PhantomShareUnitsPSUsMember_e666a3cc-0cae-43f5-9a0b-dbd25dcd0801" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_6c1b9d61-09ef-4f2d-ad4d-15c6c63179e4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7c5a7ae8-5cfe-465c-9318-3c8dab97bff3" xlink:to="loc_us-gaap_PerformanceSharesMember_6c1b9d61-09ef-4f2d-ad4d-15c6c63179e4" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/FairValueMeasurementsDetails" xlink:type="simple" xlink:href="iesc-20211231.xsd#FairValueMeasurementsDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/FairValueMeasurementsDetails" xlink:type="extended" id="ibee4951a101144a3be3e2bdb0f17d970_FairValueMeasurementsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_3d9f2995-3d1e-441e-87e0-209278d8dd2b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_228cccce-945f-4258-b8b5-b06ca997b53d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_3d9f2995-3d1e-441e-87e0-209278d8dd2b" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_228cccce-945f-4258-b8b5-b06ca997b53d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_b27d46ce-ac86-4830-a2af-f2155e58441f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_3d9f2995-3d1e-441e-87e0-209278d8dd2b" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_b27d46ce-ac86-4830-a2af-f2155e58441f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_5b64468a-d3e5-4b72-b362-688677dffb54" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_3d9f2995-3d1e-441e-87e0-209278d8dd2b" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_5b64468a-d3e5-4b72-b362-688677dffb54" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_ca18cf4d-0041-484c-a6fe-5aa46824a9eb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_3d9f2995-3d1e-441e-87e0-209278d8dd2b" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_ca18cf4d-0041-484c-a6fe-5aa46824a9eb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetAssetLiability_1bd6bbe2-7282-46bd-a2f0-88c6d36e795c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueNetAssetLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_3d9f2995-3d1e-441e-87e0-209278d8dd2b" xlink:to="loc_us-gaap_FairValueNetAssetLiability_1bd6bbe2-7282-46bd-a2f0-88c6d36e795c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_7364555f-58a3-48fb-9051-641e92daef6a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_3d9f2995-3d1e-441e-87e0-209278d8dd2b" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_7364555f-58a3-48fb-9051-641e92daef6a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_655335a4-b5d9-4c19-b8db-f189c814ee11" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_3d9f2995-3d1e-441e-87e0-209278d8dd2b" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_655335a4-b5d9-4c19-b8db-f189c814ee11" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_300015c5-3c57-4c74-bfdf-2bd738dde5e6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_655335a4-b5d9-4c19-b8db-f189c814ee11" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_300015c5-3c57-4c74-bfdf-2bd738dde5e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_300015c5-3c57-4c74-bfdf-2bd738dde5e6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_300015c5-3c57-4c74-bfdf-2bd738dde5e6" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_300015c5-3c57-4c74-bfdf-2bd738dde5e6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_020b6d8d-f2a4-40be-8b06-17dd8d61b402" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_300015c5-3c57-4c74-bfdf-2bd738dde5e6" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_020b6d8d-f2a4-40be-8b06-17dd8d61b402" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_4c0ef7e5-ee76-450c-b955-f5c6ff83a4e3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_020b6d8d-f2a4-40be-8b06-17dd8d61b402" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_4c0ef7e5-ee76-450c-b955-f5c6ff83a4e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_164406ae-7e91-4bca-90c0-807146f973bb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_020b6d8d-f2a4-40be-8b06-17dd8d61b402" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_164406ae-7e91-4bca-90c0-807146f973bb" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/GoodwillandIntangibleAssetsGoodwillDetails" xlink:type="simple" xlink:href="iesc-20211231.xsd#GoodwillandIntangibleAssetsGoodwillDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/GoodwillandIntangibleAssetsGoodwillDetails" xlink:type="extended" id="if3615255fc594fa4b9d6d3dfdfa1b2be_GoodwillandIntangibleAssetsGoodwillDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_42a04ab5-7607-4e63-afca-9d64424fb027" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_ace1ad2a-5fa2-47d2-aa0e-812d303d50bd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_42a04ab5-7607-4e63-afca-9d64424fb027" xlink:to="loc_us-gaap_Goodwill_ace1ad2a-5fa2-47d2-aa0e-812d303d50bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_24e1b060-764f-4643-9da7-9ad7c2447d93" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Goodwill"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_3b82774e-1b6d-49e1-b9c8-831c2fdc9e67" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_42a04ab5-7607-4e63-afca-9d64424fb027" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_3b82774e-1b6d-49e1-b9c8-831c2fdc9e67" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_24c6b1bd-e269-4cb2-b925-c7399450b332" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_3b82774e-1b6d-49e1-b9c8-831c2fdc9e67" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_24c6b1bd-e269-4cb2-b925-c7399450b332" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_24c6b1bd-e269-4cb2-b925-c7399450b332_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_24c6b1bd-e269-4cb2-b925-c7399450b332" xlink:to="loc_us-gaap_SegmentDomain_24c6b1bd-e269-4cb2-b925-c7399450b332_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_830522de-6630-43db-a370-5e25245c8736" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_24c6b1bd-e269-4cb2-b925-c7399450b332" xlink:to="loc_us-gaap_SegmentDomain_830522de-6630-43db-a370-5e25245c8736" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_CommercialandIndustrialMember_d20c943c-f515-4730-805e-99ad520b7768" xlink:href="iesc-20211231.xsd#iesc_CommercialandIndustrialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_830522de-6630-43db-a370-5e25245c8736" xlink:to="loc_iesc_CommercialandIndustrialMember_d20c943c-f515-4730-805e-99ad520b7768" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_ResidentialMember_77822431-1c88-4298-9ee1-c495b15076aa" xlink:href="iesc-20211231.xsd#iesc_ResidentialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_830522de-6630-43db-a370-5e25245c8736" xlink:to="loc_iesc_ResidentialMember_77822431-1c88-4298-9ee1-c495b15076aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_InfrastructureSolutionsMember_6a0e98fb-79c3-4082-967a-fbaf414c00e2" xlink:href="iesc-20211231.xsd#iesc_InfrastructureSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_830522de-6630-43db-a370-5e25245c8736" xlink:to="loc_iesc_InfrastructureSolutionsMember_6a0e98fb-79c3-4082-967a-fbaf414c00e2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_CommunicationsMember_1afe6cde-c2eb-4b16-8ec9-cad21ffd94e1" xlink:href="iesc-20211231.xsd#iesc_CommunicationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_830522de-6630-43db-a370-5e25245c8736" xlink:to="loc_iesc_CommunicationsMember_1afe6cde-c2eb-4b16-8ec9-cad21ffd94e1" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/GoodwillandIntangibleAssetsIntangiblesDetails" xlink:type="simple" xlink:href="iesc-20211231.xsd#GoodwillandIntangibleAssetsIntangiblesDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/GoodwillandIntangibleAssetsIntangiblesDetails" xlink:type="extended" id="ic0e6a1225dfd429e833a3d5aecb52f80_GoodwillandIntangibleAssetsIntangiblesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_72416c8f-5d1c-4746-b3eb-b1d318acfc72" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_d986baee-b234-44b7-9a84-27958f130cee" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_72416c8f-5d1c-4746-b3eb-b1d318acfc72" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_d986baee-b234-44b7-9a84-27958f130cee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_1e55e97e-6b17-4af2-9b86-59a1dd618e56" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_72416c8f-5d1c-4746-b3eb-b1d318acfc72" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_1e55e97e-6b17-4af2-9b86-59a1dd618e56" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_4b469b35-6b0f-4508-9567-efe302c26dc9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_72416c8f-5d1c-4746-b3eb-b1d318acfc72" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_4b469b35-6b0f-4508-9567-efe302c26dc9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_fb7ac82c-9488-45a1-bf8a-b4da0756eb20" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_72416c8f-5d1c-4746-b3eb-b1d318acfc72" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_fb7ac82c-9488-45a1-bf8a-b4da0756eb20" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_a8cbd8f3-2405-4a52-96e8-1f7495c1d6ff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_72416c8f-5d1c-4746-b3eb-b1d318acfc72" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_a8cbd8f3-2405-4a52-96e8-1f7495c1d6ff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_c66ca2bf-7d6f-4b0e-9fb4-362b1b3f5f5e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_a8cbd8f3-2405-4a52-96e8-1f7495c1d6ff" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_c66ca2bf-7d6f-4b0e-9fb4-362b1b3f5f5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c66ca2bf-7d6f-4b0e-9fb4-362b1b3f5f5e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_c66ca2bf-7d6f-4b0e-9fb4-362b1b3f5f5e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c66ca2bf-7d6f-4b0e-9fb4-362b1b3f5f5e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f1838982-8e4d-4e70-bb39-007c274efabf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_c66ca2bf-7d6f-4b0e-9fb4-362b1b3f5f5e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f1838982-8e4d-4e70-bb39-007c274efabf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksAndTradeNamesMember_a7bffcc8-b49a-42d1-9e53-24f7acf8933a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TrademarksAndTradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f1838982-8e4d-4e70-bb39-007c274efabf" xlink:to="loc_us-gaap_TrademarksAndTradeNamesMember_a7bffcc8-b49a-42d1-9e53-24f7acf8933a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_de1edc73-377a-41ec-b48c-d3ccb8d995d6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f1838982-8e4d-4e70-bb39-007c274efabf" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_de1edc73-377a-41ec-b48c-d3ccb8d995d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_bdbc29c4-3feb-4df0-bd82-16f90f07c12b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f1838982-8e4d-4e70-bb39-007c274efabf" xlink:to="loc_us-gaap_CustomerRelationshipsMember_bdbc29c4-3feb-4df0-bd82-16f90f07c12b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_06c3f30b-2594-4177-be0e-004930bc3f2a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NoncompeteAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f1838982-8e4d-4e70-bb39-007c274efabf" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_06c3f30b-2594-4177-be0e-004930bc3f2a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OrderOrProductionBacklogMember_96d5a8eb-27ec-4460-a53a-70cecffbd6b3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OrderOrProductionBacklogMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f1838982-8e4d-4e70-bb39-007c274efabf" xlink:to="loc_us-gaap_OrderOrProductionBacklogMember_96d5a8eb-27ec-4460-a53a-70cecffbd6b3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_bd3d14d7-2d40-4617-8696-73369f4b3dcc" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_a8cbd8f3-2405-4a52-96e8-1f7495c1d6ff" xlink:to="loc_srt_RangeAxis_bd3d14d7-2d40-4617-8696-73369f4b3dcc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_bd3d14d7-2d40-4617-8696-73369f4b3dcc_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_bd3d14d7-2d40-4617-8696-73369f4b3dcc" xlink:to="loc_srt_RangeMember_bd3d14d7-2d40-4617-8696-73369f4b3dcc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_9aa19f74-12ac-44b1-87aa-c27647fa05a0" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_bd3d14d7-2d40-4617-8696-73369f4b3dcc" xlink:to="loc_srt_RangeMember_9aa19f74-12ac-44b1-87aa-c27647fa05a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_007f02c6-5eda-43f4-8ec2-e7b237110466" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_9aa19f74-12ac-44b1-87aa-c27647fa05a0" xlink:to="loc_srt_MinimumMember_007f02c6-5eda-43f4-8ec2-e7b237110466" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_f45db554-e2d1-4bb3-9e9c-71c7d6f71b46" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_9aa19f74-12ac-44b1-87aa-c27647fa05a0" xlink:to="loc_srt_MaximumMember_f45db554-e2d1-4bb3-9e9c-71c7d6f71b46" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="iesc-20211231.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/CommitmentsandContingenciesDetails" xlink:type="extended" id="id979b209923f4d6db32d98b01cac54f3_CommitmentsandContingenciesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_50d68f88-236e-4e59-94a2-889f437b9962" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_fab71d57-ac9c-4120-9e7a-1aa91ce4a203" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_50d68f88-236e-4e59-94a2-889f437b9962" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_fab71d57-ac9c-4120-9e7a-1aa91ce4a203" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_d7eede85-3f7e-4a90-8dbb-1133fbfc7261" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_50d68f88-236e-4e59-94a2-889f437b9962" xlink:to="loc_us-gaap_LossContingenciesTable_d7eede85-3f7e-4a90-8dbb-1133fbfc7261" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_49dfdc31-5e89-40b8-93ed-1079d4d97cd6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_d7eede85-3f7e-4a90-8dbb-1133fbfc7261" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_49dfdc31-5e89-40b8-93ed-1079d4d97cd6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_49dfdc31-5e89-40b8-93ed-1079d4d97cd6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_49dfdc31-5e89-40b8-93ed-1079d4d97cd6" xlink:to="loc_us-gaap_LossContingencyNatureDomain_49dfdc31-5e89-40b8-93ed-1079d4d97cd6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_9419b733-8b48-492d-983f-6bd2776d9709" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_49dfdc31-5e89-40b8-93ed-1079d4d97cd6" xlink:to="loc_us-gaap_LossContingencyNatureDomain_9419b733-8b48-492d-983f-6bd2776d9709" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_InsuranceRelatedMember_00f56ecc-b091-433f-afba-99135bbad616" xlink:href="iesc-20211231.xsd#iesc_InsuranceRelatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_9419b733-8b48-492d-983f-6bd2776d9709" xlink:to="loc_iesc_InsuranceRelatedMember_00f56ecc-b091-433f-afba-99135bbad616" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
