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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:92bd74d3-ab6d-4eb1-9a53-b98f77b7f15a,g:8d53422b-a313-49bc-a5a2-012650db22cf-->
<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-20250331.xsd#DEIDocument"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/DEIDocument" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_32a997a1-348b-4520-9913-a106d81bc386" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntitiesTable_32a997a1-348b-4520-9913-a106d81bc386" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_abee5e20-b1ff-469d-a3ec-ffeaf11b15d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_32a997a1-348b-4520-9913-a106d81bc386" xlink:to="loc_us-gaap_StatementClassOfStockAxis_abee5e20-b1ff-469d-a3ec-ffeaf11b15d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_abee5e20-b1ff-469d-a3ec-ffeaf11b15d8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_abee5e20-b1ff-469d-a3ec-ffeaf11b15d8" xlink:to="loc_us-gaap_ClassOfStockDomain_abee5e20-b1ff-469d-a3ec-ffeaf11b15d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_fc56257b-66e6-49ad-ac68-467aa016ee67" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_abee5e20-b1ff-469d-a3ec-ffeaf11b15d8" xlink:to="loc_us-gaap_ClassOfStockDomain_fc56257b-66e6-49ad-ac68-467aa016ee67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_cdc85d3f-2a30-4cfb-83ad-de3eeb9ae653" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_fc56257b-66e6-49ad-ac68-467aa016ee67" xlink:to="loc_us-gaap_CommonStockMember_cdc85d3f-2a30-4cfb-83ad-de3eeb9ae653" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_7f7fbfd8-29d3-4caf-a0ea-60602445c03d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityFileNumber_7f7fbfd8-29d3-4caf-a0ea-60602445c03d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_0ddeafef-7fa1-46c8-b0b6-31ddde5cfff5" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityRegistrantName_0ddeafef-7fa1-46c8-b0b6-31ddde5cfff5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_ae18a493-e24f-4a56-8be6-7d3ddc24d083" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_DocumentPeriodEndDate_ae18a493-e24f-4a56-8be6-7d3ddc24d083" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_bb9d3cdf-ae16-4a52-973c-39ca26693263" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_DocumentQuarterlyReport_bb9d3cdf-ae16-4a52-973c-39ca26693263" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_2a5cc6f7-c40f-4882-b8b4-3315fb718742" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_DocumentTransitionReport_2a5cc6f7-c40f-4882-b8b4-3315fb718742" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_8344f994-34fc-4e43-88a8-086e9f6fa2ae" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityCentralIndexKey_8344f994-34fc-4e43-88a8-086e9f6fa2ae" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_a78c9efe-17cf-455a-beab-03f4364caed0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityIncorporationStateCountryCode_a78c9efe-17cf-455a-beab-03f4364caed0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_a6f0dabb-9903-42e4-91ca-fa82a175accb" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_DocumentType_a6f0dabb-9903-42e4-91ca-fa82a175accb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_8935e413-58de-43ae-9d73-9ff9f9b16db4" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_AmendmentFlag_8935e413-58de-43ae-9d73-9ff9f9b16db4" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_e3bc329e-e65c-49ec-9bd0-94aadc506705" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_DocumentFiscalYearFocus_e3bc329e-e65c-49ec-9bd0-94aadc506705" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_9c5ad0b8-544a-417a-9d42-51b626d6dba5" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_DocumentFiscalPeriodFocus_9c5ad0b8-544a-417a-9d42-51b626d6dba5" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_a3cb60c2-33d9-4fdb-8c42-870c061198ba" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_CurrentFiscalYearEndDate_a3cb60c2-33d9-4fdb-8c42-870c061198ba" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_733983bb-a2e5-446b-bf79-a5155385ef18" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityFilerCategory_733983bb-a2e5-446b-bf79-a5155385ef18" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_64f57c6c-8180-4dba-91e6-2a58ae31ef78" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityTaxIdentificationNumber_64f57c6c-8180-4dba-91e6-2a58ae31ef78" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_7e8bf17e-883e-46c2-bba2-eb36a21d28d2" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_Security12bTitle_7e8bf17e-883e-46c2-bba2-eb36a21d28d2" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_61033b99-7f24-4fd9-b951-f58497da4a8c" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_TradingSymbol_61033b99-7f24-4fd9-b951-f58497da4a8c" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_6d81874b-a5cb-4251-a5a3-73d0a1b1832f" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_SecurityExchangeName_6d81874b-a5cb-4251-a5a3-73d0a1b1832f" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_1d749a9f-db54-4a96-aedb-d48fc6f37ce7" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityCurrentReportingStatus_1d749a9f-db54-4a96-aedb-d48fc6f37ce7" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_2a6600ca-9ca8-43ee-b15e-01c64c62a76a" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityInteractiveDataCurrent_2a6600ca-9ca8-43ee-b15e-01c64c62a76a" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_d2fea824-7739-43f5-9918-3335d385c337" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityShellCompany_d2fea824-7739-43f5-9918-3335d385c337" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_ef148cc7-2e07-4f66-bc37-bf954ca46f54" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntitySmallBusiness_ef148cc7-2e07-4f66-bc37-bf954ca46f54" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_a1ef5233-6755-4bd7-aecc-2f5f58047b54" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityEmergingGrowthCompany_a1ef5233-6755-4bd7-aecc-2f5f58047b54" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_1d4eec03-d720-4a4a-9f04-7e6969509a59" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityAddressAddressLine1_1d4eec03-d720-4a4a-9f04-7e6969509a59" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_b418b297-2edd-4d79-8da5-13d3acf12e80" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityAddressAddressLine2_b418b297-2edd-4d79-8da5-13d3acf12e80" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_1b359193-fac8-4256-9c42-d055b945a5eb" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityAddressCityOrTown_1b359193-fac8-4256-9c42-d055b945a5eb" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_2a326b44-7357-4455-a8d7-c58ffb5d539f" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityAddressStateOrProvince_2a326b44-7357-4455-a8d7-c58ffb5d539f" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_3854dd0f-b692-4e90-832a-64073735d540" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityAddressPostalZipCode_3854dd0f-b692-4e90-832a-64073735d540" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_4ae9b8ba-9f5c-42c7-9e76-ef1273ddf0f8" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_CityAreaCode_4ae9b8ba-9f5c-42c7-9e76-ef1273ddf0f8" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_a983159d-dac6-4e19-8828-b1fa4b01c3b0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_LocalPhoneNumber_a983159d-dac6-4e19-8828-b1fa4b01c3b0" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_511e5cef-7499-4c6c-9e2c-67f702a483c6" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_d5366198-7abe-43ba-b470-0037ad428363" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_511e5cef-7499-4c6c-9e2c-67f702a483c6" xlink:type="arc" order="29"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/ConsolidatedStatementsofStockholdersEquity" xlink:type="simple" xlink:href="iesc-20250331.xsd#ConsolidatedStatementsofStockholdersEquity"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/ConsolidatedStatementsofStockholdersEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_c9e00a97-2e65-4cb7-963b-4ecb684a7294" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_StatementTable_c9e00a97-2e65-4cb7-963b-4ecb684a7294" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_81209d69-e00e-4b05-a137-1f81137c3acd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_c9e00a97-2e65-4cb7-963b-4ecb684a7294" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_81209d69-e00e-4b05-a137-1f81137c3acd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_81209d69-e00e-4b05-a137-1f81137c3acd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_81209d69-e00e-4b05-a137-1f81137c3acd" xlink:to="loc_us-gaap_EquityComponentDomain_81209d69-e00e-4b05-a137-1f81137c3acd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_e5fe65d8-4ea3-4f35-a1c8-f07bd62803b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_81209d69-e00e-4b05-a137-1f81137c3acd" xlink:to="loc_us-gaap_EquityComponentDomain_e5fe65d8-4ea3-4f35-a1c8-f07bd62803b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_fb9b02e5-8aee-4c5a-a5d5-c8121863fc36" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_e5fe65d8-4ea3-4f35-a1c8-f07bd62803b8" xlink:to="loc_us-gaap_CommonStockMember_fb9b02e5-8aee-4c5a-a5d5-c8121863fc36" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_39fd27cc-65ed-42c8-9769-2dcaccc6b0e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_e5fe65d8-4ea3-4f35-a1c8-f07bd62803b8" xlink:to="loc_us-gaap_TreasuryStockCommonMember_39fd27cc-65ed-42c8-9769-2dcaccc6b0e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_ecf0da79-c14b-404b-bf55-1b017cba2580" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_e5fe65d8-4ea3-4f35-a1c8-f07bd62803b8" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_ecf0da79-c14b-404b-bf55-1b017cba2580" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_67b44ce2-d2ae-4684-8bbf-5b10218a45c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_e5fe65d8-4ea3-4f35-a1c8-f07bd62803b8" xlink:to="loc_us-gaap_RetainedEarningsMember_67b44ce2-d2ae-4684-8bbf-5b10218a45c7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_c392962d-67ad-464f-ab4a-f03219041f0b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_398f86e5-8871-4c4b-912f-410c627a2fff" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CumulativeEffectPeriodOfAdoptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_c9e00a97-2e65-4cb7-963b-4ecb684a7294" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_398f86e5-8871-4c4b-912f-410c627a2fff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_398f86e5-8871-4c4b-912f-410c627a2fff_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_398f86e5-8871-4c4b-912f-410c627a2fff" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_398f86e5-8871-4c4b-912f-410c627a2fff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_a089710c-be60-4483-ac48-88c1419b31f7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_398f86e5-8871-4c4b-912f-410c627a2fff" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_a089710c-be60-4483-ac48-88c1419b31f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_d6f74cbb-1cf1-4065-9628-c4211360a74b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_a089710c-be60-4483-ac48-88c1419b31f7" xlink:to="loc_us-gaap_RetainedEarningsMember_d6f74cbb-1cf1-4065-9628-c4211360a74b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_3c155d60-9cbc-4b9a-a3eb-5e759591c111" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_StockholdersEquity_3c155d60-9cbc-4b9a-a3eb-5e759591c111" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_0905c1be-b945-477b-b819-9badd3d1c8fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_SharesIssued_0905c1be-b945-477b-b819-9badd3d1c8fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_63e4cae8-58bc-4777-9b96-bc3313cec409" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_63e4cae8-58bc-4777-9b96-bc3313cec409" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_3232619a-c9c2-48fb-ac5e-94a13596118c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_3232619a-c9c2-48fb-ac5e-94a13596118c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_7be7ad43-8591-46cb-99af-eae1736fbd48" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_7be7ad43-8591-46cb-99af-eae1736fbd48" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_e13f5af6-5401-4a69-ac9c-1940716b0f19" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_e13f5af6-5401-4a69-ac9c-1940716b0f19" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_b4fb40b4-262b-434e-8945-876ea632c087" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_b4fb40b4-262b-434e-8945-876ea632c087" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_f9f58aae-68f5-46fc-bd71-f7376452a0fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_f9f58aae-68f5-46fc-bd71-f7376452a0fe" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_d1061b54-f366-4e9f-9339-3533db4d1e9a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_d1061b54-f366-4e9f-9339-3533db4d1e9a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityPeriodIncreaseDecrease_2ff620c9-d788-43f1-9a71-f64d68e3f9d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityPeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_StockholdersEquityPeriodIncreaseDecrease_2ff620c9-d788-43f1-9a71-f64d68e3f9d8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_a078394d-c9eb-4a41-bf8c-5260952473ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_ProfitLoss_a078394d-c9eb-4a41-bf8c-5260952473ae" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalOther_ff2d9571-28a6-4114-86ca-fc278154ec1e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalOther_ff2d9571-28a6-4114-86ca-fc278154ec1e" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestChangeInRedemptionValue_0ca25cf3-43b9-44fb-bb0f-076816a12d4a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MinorityInterestChangeInRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_MinorityInterestChangeInRedemptionValue_0ca25cf3-43b9-44fb-bb0f-076816a12d4a" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_f8c7b191-d011-4f60-948f-33e848dc1ccd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_b40c90d7-1d72-43bf-842d-b40afc354671" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_7b9a65c5-0d21-485f-bf83-fb6cdb668a37" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_7b9a65c5-0d21-485f-bf83-fb6cdb668a37" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_481dcd25-0105-480c-a18a-c971503addfe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6f26b133-1175-4005-98b2-19104ca802e0" xlink:to="loc_us-gaap_TreasuryStockCommonShares_481dcd25-0105-480c-a18a-c971503addfe" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/BusinessDetails" xlink:type="simple" xlink:href="iesc-20250331.xsd#BusinessDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/BusinessDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestLineItems_4654a0d4-f07a-4ec9-b7e0-ff4538e1974d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RedeemableNoncontrollingInterestLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestByLegalEntityTable_7e5b883d-cc0d-4016-a55b-bb27d75ac95b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RedeemableNoncontrollingInterestByLegalEntityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RedeemableNoncontrollingInterestLineItems_4654a0d4-f07a-4ec9-b7e0-ff4538e1974d" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestByLegalEntityTable_7e5b883d-cc0d-4016-a55b-bb27d75ac95b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestDecreaseFromRedemptions_c44467a1-0b1c-477c-a25d-fd85b65fb374" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MinorityInterestDecreaseFromRedemptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RedeemableNoncontrollingInterestLineItems_4654a0d4-f07a-4ec9-b7e0-ff4538e1974d" xlink:to="loc_us-gaap_MinorityInterestDecreaseFromRedemptions_c44467a1-0b1c-477c-a25d-fd85b65fb374" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRepurchaseOfRedeemableNoncontrollingInterest_1b13fb0b-5649-4109-8740-912159e5ba1e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForRepurchaseOfRedeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RedeemableNoncontrollingInterestLineItems_4654a0d4-f07a-4ec9-b7e0-ff4538e1974d" xlink:to="loc_us-gaap_PaymentsForRepurchaseOfRedeemableNoncontrollingInterest_1b13fb0b-5649-4109-8740-912159e5ba1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_2823a047-7f0a-4430-9e4f-fc65117f3ad9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RedeemableNoncontrollingInterestLineItems_4654a0d4-f07a-4ec9-b7e0-ff4538e1974d" xlink:to="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_2823a047-7f0a-4430-9e4f-fc65117f3ad9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToMinorityShareholders_204abef1-284a-47c6-b62a-03785e15f25e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToMinorityShareholders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RedeemableNoncontrollingInterestLineItems_4654a0d4-f07a-4ec9-b7e0-ff4538e1974d" xlink:to="loc_us-gaap_PaymentsToMinorityShareholders_204abef1-284a-47c6-b62a-03785e15f25e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestChangeInRedemptionValue_341e7b92-8127-4739-a3da-56d19c1a6489" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MinorityInterestChangeInRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RedeemableNoncontrollingInterestLineItems_4654a0d4-f07a-4ec9-b7e0-ff4538e1974d" xlink:to="loc_us-gaap_MinorityInterestChangeInRedemptionValue_341e7b92-8127-4739-a3da-56d19c1a6489" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestChangesPurchaseOfInterestByParent_0ed411bf-ec0c-45f2-8a0e-915c804f5638" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestChangesPurchaseOfInterestByParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RedeemableNoncontrollingInterestLineItems_4654a0d4-f07a-4ec9-b7e0-ff4538e1974d" xlink:to="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestChangesPurchaseOfInterestByParent_0ed411bf-ec0c-45f2-8a0e-915c804f5638" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_b08e1779-9068-4e83-ae94-959b4e698f09" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RedeemableNoncontrollingInterestLineItems_4654a0d4-f07a-4ec9-b7e0-ff4538e1974d" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_b08e1779-9068-4e83-ae94-959b4e698f09" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_fdbc1b23-ed49-47a2-a382-d457eeba3b83" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_3c07544d-c4c4-4766-8cac-2571742cbbab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_fdbc1b23-ed49-47a2-a382-d457eeba3b83" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_3c07544d-c4c4-4766-8cac-2571742cbbab" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_1387a82c-76b6-4130-be86-542b91a6c241" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_3c07544d-c4c4-4766-8cac-2571742cbbab" xlink:to="loc_srt_RangeAxis_1387a82c-76b6-4130-be86-542b91a6c241" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1387a82c-76b6-4130-be86-542b91a6c241_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_1387a82c-76b6-4130-be86-542b91a6c241" xlink:to="loc_srt_RangeMember_1387a82c-76b6-4130-be86-542b91a6c241_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_ca1ab7c9-bb48-4a22-950d-255162cf6259" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_1387a82c-76b6-4130-be86-542b91a6c241" xlink:to="loc_srt_RangeMember_ca1ab7c9-bb48-4a22-950d-255162cf6259" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_b4b5b04c-e509-4bf3-b5e0-e444b21c41cc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_ca1ab7c9-bb48-4a22-950d-255162cf6259" xlink:to="loc_srt_MinimumMember_b4b5b04c-e509-4bf3-b5e0-e444b21c41cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_a38db932-d0ac-44aa-a8aa-90767805c7c6" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_3c07544d-c4c4-4766-8cac-2571742cbbab" xlink:to="loc_dei_LegalEntityAxis_a38db932-d0ac-44aa-a8aa-90767805c7c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a38db932-d0ac-44aa-a8aa-90767805c7c6_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_a38db932-d0ac-44aa-a8aa-90767805c7c6" xlink:to="loc_dei_EntityDomain_a38db932-d0ac-44aa-a8aa-90767805c7c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_5c9aab32-567a-4a7d-9b2c-2a2c13012220" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_a38db932-d0ac-44aa-a8aa-90767805c7c6" xlink:to="loc_dei_EntityDomain_5c9aab32-567a-4a7d-9b2c-2a2c13012220" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_IncorporatedInvesteeMember_fb54efd0-d156-406f-bece-5de92192387e" xlink:href="iesc-20250331.xsd#iesc_IncorporatedInvesteeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5c9aab32-567a-4a7d-9b2c-2a2c13012220" xlink:to="loc_iesc_IncorporatedInvesteeMember_fb54efd0-d156-406f-bece-5de92192387e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_561806dc-4bc5-4093-b7e6-37e8ef0d5b70" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_fdbc1b23-ed49-47a2-a382-d457eeba3b83" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_561806dc-4bc5-4093-b7e6-37e8ef0d5b70" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/RevenueRecognitionDetails" xlink:type="simple" xlink:href="iesc-20250331.xsd#RevenueRecognitionDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/RevenueRecognitionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_2ad92b74-632c-41a1-8a2d-d5095105b53f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_bf0ab1c2-b775-48f3-91e3-72ef057f2e68" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2ad92b74-632c-41a1-8a2d-d5095105b53f" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_bf0ab1c2-b775-48f3-91e3-72ef057f2e68" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_23e0ab23-9286-4b67-a8c5-5cdb647c4f57" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_bf0ab1c2-b775-48f3-91e3-72ef057f2e68" xlink:to="loc_srt_ProductOrServiceAxis_23e0ab23-9286-4b67-a8c5-5cdb647c4f57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_23e0ab23-9286-4b67-a8c5-5cdb647c4f57_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_23e0ab23-9286-4b67-a8c5-5cdb647c4f57" xlink:to="loc_srt_ProductsAndServicesDomain_23e0ab23-9286-4b67-a8c5-5cdb647c4f57_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_6b070bd5-81fa-4203-90fa-15335d1be2c4" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_23e0ab23-9286-4b67-a8c5-5cdb647c4f57" xlink:to="loc_srt_ProductsAndServicesDomain_6b070bd5-81fa-4203-90fa-15335d1be2c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_IndustrialServicesMember_336d4aa3-c6b8-4a21-9c4d-0967dd7d8103" xlink:href="iesc-20250331.xsd#iesc_IndustrialServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_6b070bd5-81fa-4203-90fa-15335d1be2c4" xlink:to="loc_iesc_IndustrialServicesMember_336d4aa3-c6b8-4a21-9c4d-0967dd7d8103" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_CustomEngineeredSolutionsMember_d028c07c-0072-442f-878a-454e8d809ddc" xlink:href="iesc-20250331.xsd#iesc_CustomEngineeredSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_6b070bd5-81fa-4203-90fa-15335d1be2c4" xlink:to="loc_iesc_CustomEngineeredSolutionsMember_d028c07c-0072-442f-878a-454e8d809ddc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_SingleFamilyElectricalContractsMember_5b4e0d35-648f-4fe7-a707-24547a251951" xlink:href="iesc-20250331.xsd#iesc_SingleFamilyElectricalContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_6b070bd5-81fa-4203-90fa-15335d1be2c4" xlink:to="loc_iesc_SingleFamilyElectricalContractsMember_5b4e0d35-648f-4fe7-a707-24547a251951" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_MultiFamilyandOtherMember_90644c06-8fb8-462a-8d38-b897c6b9ecc6" xlink:href="iesc-20250331.xsd#iesc_MultiFamilyandOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_6b070bd5-81fa-4203-90fa-15335d1be2c4" xlink:to="loc_iesc_MultiFamilyandOtherMember_90644c06-8fb8-462a-8d38-b897c6b9ecc6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_SingleFamilyContractsPlumbingHVACMember_e986977d-2e27-44c0-aa83-32d1943a01eb" xlink:href="iesc-20250331.xsd#iesc_SingleFamilyContractsPlumbingHVACMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_6b070bd5-81fa-4203-90fa-15335d1be2c4" xlink:to="loc_iesc_SingleFamilyContractsPlumbingHVACMember_e986977d-2e27-44c0-aa83-32d1943a01eb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_e99882f0-e9b5-4d2a-a9e4-7737473db44c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerBasisOfPricingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_bf0ab1c2-b775-48f3-91e3-72ef057f2e68" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_e99882f0-e9b5-4d2a-a9e4-7737473db44c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_e99882f0-e9b5-4d2a-a9e4-7737473db44c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerBasisOfPricingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_e99882f0-e9b5-4d2a-a9e4-7737473db44c" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_e99882f0-e9b5-4d2a-a9e4-7737473db44c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_f415435b-5ef4-4134-8490-ac1ca4e956d7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerBasisOfPricingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_e99882f0-e9b5-4d2a-a9e4-7737473db44c" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_f415435b-5ef4-4134-8490-ac1ca4e956d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedPriceContractMember_5c96c91e-d478-469c-8879-991b74b2d7ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FixedPriceContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_f415435b-5ef4-4134-8490-ac1ca4e956d7" xlink:to="loc_us-gaap_FixedPriceContractMember_5c96c91e-d478-469c-8879-991b74b2d7ae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimeAndMaterialsContractMember_5238a552-a6a2-4107-8b55-e8a606b37bd5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TimeAndMaterialsContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_f415435b-5ef4-4134-8490-ac1ca4e956d7" xlink:to="loc_us-gaap_TimeAndMaterialsContractMember_5238a552-a6a2-4107-8b55-e8a606b37bd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_cbc8a745-1933-46b1-a2e6-de89dff1998f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_bf0ab1c2-b775-48f3-91e3-72ef057f2e68" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_cbc8a745-1933-46b1-a2e6-de89dff1998f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_cbc8a745-1933-46b1-a2e6-de89dff1998f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_cbc8a745-1933-46b1-a2e6-de89dff1998f" xlink:to="loc_us-gaap_SegmentDomain_cbc8a745-1933-46b1-a2e6-de89dff1998f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_69a535fe-1b23-43e5-b063-366e59ddf922" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_cbc8a745-1933-46b1-a2e6-de89dff1998f" xlink:to="loc_us-gaap_SegmentDomain_69a535fe-1b23-43e5-b063-366e59ddf922" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_CommercialandIndustrialMember_9bcc453d-5e68-4ccf-9d1f-c5896037db2c" xlink:href="iesc-20250331.xsd#iesc_CommercialandIndustrialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_69a535fe-1b23-43e5-b063-366e59ddf922" xlink:to="loc_iesc_CommercialandIndustrialMember_9bcc453d-5e68-4ccf-9d1f-c5896037db2c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_CommunicationsMember_d868c9a5-2d8c-49ab-838b-94738ddf1cd3" xlink:href="iesc-20250331.xsd#iesc_CommunicationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_69a535fe-1b23-43e5-b063-366e59ddf922" xlink:to="loc_iesc_CommunicationsMember_d868c9a5-2d8c-49ab-838b-94738ddf1cd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_InfrastructureSolutionsMember_7b79ace5-225b-4333-9678-aa40458c7488" xlink:href="iesc-20250331.xsd#iesc_InfrastructureSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_69a535fe-1b23-43e5-b063-366e59ddf922" xlink:to="loc_iesc_InfrastructureSolutionsMember_7b79ace5-225b-4333-9678-aa40458c7488" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_ResidentialMember_3a17ee4e-91e2-493a-9e6d-3c37dc26e56e" xlink:href="iesc-20250331.xsd#iesc_ResidentialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_69a535fe-1b23-43e5-b063-366e59ddf922" xlink:to="loc_iesc_ResidentialMember_3a17ee4e-91e2-493a-9e6d-3c37dc26e56e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_025362c5-3cf9-4437-bf19-f10685531fdf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2ad92b74-632c-41a1-8a2d-d5095105b53f" xlink:to="loc_us-gaap_Revenues_025362c5-3cf9-4437-bf19-f10685531fdf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_67760ccf-37d9-4bd7-8e90-78f3ae480b86" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2ad92b74-632c-41a1-8a2d-d5095105b53f" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_67760ccf-37d9-4bd7-8e90-78f3ae480b86" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/DebtDetails" xlink:type="simple" xlink:href="iesc-20250331.xsd#DebtDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/DebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_7b8b71f5-c55c-4feb-8df9-48f4a602b1d0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_e75738a7-b7fa-432d-80fe-32530f765229" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_7b8b71f5-c55c-4feb-8df9-48f4a602b1d0" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_e75738a7-b7fa-432d-80fe-32530f765229" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_1819ad58-85cd-4f32-accf-1b3c94eeeebe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_e75738a7-b7fa-432d-80fe-32530f765229" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_1819ad58-85cd-4f32-accf-1b3c94eeeebe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_1819ad58-85cd-4f32-accf-1b3c94eeeebe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_1819ad58-85cd-4f32-accf-1b3c94eeeebe" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_1819ad58-85cd-4f32-accf-1b3c94eeeebe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_d83f722a-86f9-4a98-a4e5-c0d1db467777" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_1819ad58-85cd-4f32-accf-1b3c94eeeebe" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_d83f722a-86f9-4a98-a4e5-c0d1db467777" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_6b589d24-7086-4774-ad26-b48c17635061" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_d83f722a-86f9-4a98-a4e5-c0d1db467777" xlink:to="loc_us-gaap_SubsequentEventMember_6b589d24-7086-4774-ad26-b48c17635061" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_dec3b3a9-0281-427d-bae5-cd8309cd0cdb" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_e75738a7-b7fa-432d-80fe-32530f765229" xlink:to="loc_srt_RangeAxis_dec3b3a9-0281-427d-bae5-cd8309cd0cdb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_dec3b3a9-0281-427d-bae5-cd8309cd0cdb_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_dec3b3a9-0281-427d-bae5-cd8309cd0cdb" xlink:to="loc_srt_RangeMember_dec3b3a9-0281-427d-bae5-cd8309cd0cdb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_8b9a0d29-dc50-4797-9d18-62a0cf630cd9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_dec3b3a9-0281-427d-bae5-cd8309cd0cdb" xlink:to="loc_srt_RangeMember_8b9a0d29-dc50-4797-9d18-62a0cf630cd9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_8a292027-f139-43c5-9ec9-83dde911ca33" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_8b9a0d29-dc50-4797-9d18-62a0cf630cd9" xlink:to="loc_srt_MinimumMember_8a292027-f139-43c5-9ec9-83dde911ca33" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_84af60cf-9aa3-40e4-8d48-913df1c81a8f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_8b9a0d29-dc50-4797-9d18-62a0cf630cd9" xlink:to="loc_srt_MaximumMember_84af60cf-9aa3-40e4-8d48-913df1c81a8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCovenantTerms_3fd1cc87-21fc-4f93-9254-3abc64888820" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityCovenantTerms"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_7b8b71f5-c55c-4feb-8df9-48f4a602b1d0" xlink:to="loc_us-gaap_LineOfCreditFacilityCovenantTerms_3fd1cc87-21fc-4f93-9254-3abc64888820" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_ConsolidatedTotalLeverageRatioMaximum_14ad01a0-8909-451d-b45e-52635271a2bb" xlink:href="iesc-20250331.xsd#iesc_ConsolidatedTotalLeverageRatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_7b8b71f5-c55c-4feb-8df9-48f4a602b1d0" xlink:to="loc_iesc_ConsolidatedTotalLeverageRatioMaximum_14ad01a0-8909-451d-b45e-52635271a2bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_ConsolidatedInterestCoverageRatioMinimum_d7027ab8-38c4-4714-b54e-a2fadc7d5c19" xlink:href="iesc-20250331.xsd#iesc_ConsolidatedInterestCoverageRatioMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_7b8b71f5-c55c-4feb-8df9-48f4a602b1d0" xlink:to="loc_iesc_ConsolidatedInterestCoverageRatioMinimum_d7027ab8-38c4-4714-b54e-a2fadc7d5c19" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_19b8345b-9371-4dc9-849e-8b9e0f440aed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_7b8b71f5-c55c-4feb-8df9-48f4a602b1d0" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_19b8345b-9371-4dc9-849e-8b9e0f440aed" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_50b6b9b8-d357-44db-a551-a9ae4f29cec1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_7b8b71f5-c55c-4feb-8df9-48f4a602b1d0" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_50b6b9b8-d357-44db-a551-a9ae4f29cec1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_ConsolidatedTotalLeverageRatioRestrictiveCovenant_0f0a4e11-2d4d-4189-95ef-26034e754ab5" xlink:href="iesc-20250331.xsd#iesc_ConsolidatedTotalLeverageRatioRestrictiveCovenant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_7b8b71f5-c55c-4feb-8df9-48f4a602b1d0" xlink:to="loc_iesc_ConsolidatedTotalLeverageRatioRestrictiveCovenant_0f0a4e11-2d4d-4189-95ef-26034e754ab5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityInitiationDate1_5521de18-c8ba-4c2c-879d-6ab61bd78c3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityInitiationDate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_7b8b71f5-c55c-4feb-8df9-48f4a602b1d0" xlink:to="loc_us-gaap_LineOfCreditFacilityInitiationDate1_5521de18-c8ba-4c2c-879d-6ab61bd78c3e" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/PerShareInformationDetails" xlink:type="simple" xlink:href="iesc-20250331.xsd#PerShareInformationDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/PerShareInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_686c75fa-ca5a-46dd-881e-e74e9827a47f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_abe82d21-c2be-425f-b0a1-46367ca00036" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_686c75fa-ca5a-46dd-881e-e74e9827a47f" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_abe82d21-c2be-425f-b0a1-46367ca00036" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_952675eb-b887-45aa-b62f-4fa73e7140ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_abe82d21-c2be-425f-b0a1-46367ca00036" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_952675eb-b887-45aa-b62f-4fa73e7140ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_952675eb-b887-45aa-b62f-4fa73e7140ea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_952675eb-b887-45aa-b62f-4fa73e7140ea" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_952675eb-b887-45aa-b62f-4fa73e7140ea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_3f108153-72cc-4cf4-93a8-c9cef6798321" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_952675eb-b887-45aa-b62f-4fa73e7140ea" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_3f108153-72cc-4cf4-93a8-c9cef6798321" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PhantomShareUnitsPSUsMember_7fbdcb31-b083-4540-b0a3-224ba013e19d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PhantomShareUnitsPSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_3f108153-72cc-4cf4-93a8-c9cef6798321" xlink:to="loc_us-gaap_PhantomShareUnitsPSUsMember_7fbdcb31-b083-4540-b0a3-224ba013e19d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_3a5f88c0-ce63-4964-91aa-84a24efb1e7f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_686c75fa-ca5a-46dd-881e-e74e9827a47f" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_3a5f88c0-ce63-4964-91aa-84a24efb1e7f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/OperatingSegmentsDetails" xlink:type="simple" xlink:href="iesc-20250331.xsd#OperatingSegmentsDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/OperatingSegmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_b2fb77e2-4208-4d39-9f70-a32c17675828" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_8c1cbae9-9af5-412f-81c4-47c083e196bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b2fb77e2-4208-4d39-9f70-a32c17675828" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_8c1cbae9-9af5-412f-81c4-47c083e196bf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_84afa0b3-441c-4ec7-8e96-8f15be1e931d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_8c1cbae9-9af5-412f-81c4-47c083e196bf" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_84afa0b3-441c-4ec7-8e96-8f15be1e931d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_84afa0b3-441c-4ec7-8e96-8f15be1e931d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_84afa0b3-441c-4ec7-8e96-8f15be1e931d" xlink:to="loc_us-gaap_SegmentDomain_84afa0b3-441c-4ec7-8e96-8f15be1e931d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_79c8771d-5299-4e10-b103-4241faa5f5ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_84afa0b3-441c-4ec7-8e96-8f15be1e931d" xlink:to="loc_us-gaap_SegmentDomain_79c8771d-5299-4e10-b103-4241faa5f5ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_CommercialandIndustrialMember_8be6f080-fa5d-4c7b-a434-b654bec16e7f" xlink:href="iesc-20250331.xsd#iesc_CommercialandIndustrialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_79c8771d-5299-4e10-b103-4241faa5f5ff" xlink:to="loc_iesc_CommercialandIndustrialMember_8be6f080-fa5d-4c7b-a434-b654bec16e7f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_CommunicationsMember_4523facc-5c0c-467e-845e-ee42590291c9" xlink:href="iesc-20250331.xsd#iesc_CommunicationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_79c8771d-5299-4e10-b103-4241faa5f5ff" xlink:to="loc_iesc_CommunicationsMember_4523facc-5c0c-467e-845e-ee42590291c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_InfrastructureSolutionsMember_b99fee3e-e583-4029-a8ff-58dfdf3fbeb7" xlink:href="iesc-20250331.xsd#iesc_InfrastructureSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_79c8771d-5299-4e10-b103-4241faa5f5ff" xlink:to="loc_iesc_InfrastructureSolutionsMember_b99fee3e-e583-4029-a8ff-58dfdf3fbeb7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_ResidentialMember_f6d51115-9ea8-4741-aa98-6e06c249f054" xlink:href="iesc-20250331.xsd#iesc_ResidentialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_79c8771d-5299-4e10-b103-4241faa5f5ff" xlink:to="loc_iesc_ResidentialMember_f6d51115-9ea8-4741-aa98-6e06c249f054" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateMember_b82275f1-d50b-4d3a-b8a8-065ad024cd06" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_79c8771d-5299-4e10-b103-4241faa5f5ff" xlink:to="loc_us-gaap_CorporateMember_b82275f1-d50b-4d3a-b8a8-065ad024cd06" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_a72b0c41-e331-4bd5-9ea7-1c412489d681" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b2fb77e2-4208-4d39-9f70-a32c17675828" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_a72b0c41-e331-4bd5-9ea7-1c412489d681" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_02647027-3d72-41fa-bb06-4e97d232399d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b2fb77e2-4208-4d39-9f70-a32c17675828" xlink:to="loc_us-gaap_GrossProfit_02647027-3d72-41fa-bb06-4e97d232399d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_75a6d292-f090-421f-bfe4-99b8e6c5ee3b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b2fb77e2-4208-4d39-9f70-a32c17675828" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_75a6d292-f090-421f-bfe4-99b8e6c5ee3b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationIntegrationRelatedCosts_6e5b46c0-5a62-4e7c-a875-5e4bb454a51a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationIntegrationRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b2fb77e2-4208-4d39-9f70-a32c17675828" xlink:to="loc_us-gaap_BusinessCombinationIntegrationRelatedCosts_6e5b46c0-5a62-4e7c-a875-5e4bb454a51a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDispositionOfAssets1_0d04af28-3fb8-4ee3-b92c-7832784f4677" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainLossOnDispositionOfAssets1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b2fb77e2-4208-4d39-9f70-a32c17675828" xlink:to="loc_us-gaap_GainLossOnDispositionOfAssets1_0d04af28-3fb8-4ee3-b92c-7832784f4677" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_85c0ff95-043e-41e8-9851-c908d94ddb15" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b2fb77e2-4208-4d39-9f70-a32c17675828" xlink:to="loc_us-gaap_OperatingIncomeLoss_85c0ff95-043e-41e8-9851-c908d94ddb15" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_b516ba27-64b6-4963-b104-1346d227824e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b2fb77e2-4208-4d39-9f70-a32c17675828" xlink:to="loc_us-gaap_Depreciation_b516ba27-64b6-4963-b104-1346d227824e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireProductiveAssets_fccb2537-8bf6-4cb5-8f14-4919cee0b879" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireProductiveAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b2fb77e2-4208-4d39-9f70-a32c17675828" xlink:to="loc_us-gaap_PaymentsToAcquireProductiveAssets_fccb2537-8bf6-4cb5-8f14-4919cee0b879" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_6a26cc41-29d1-4c28-bef9-bef2cbf0f0c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b2fb77e2-4208-4d39-9f70-a32c17675828" xlink:to="loc_us-gaap_Assets_6a26cc41-29d1-4c28-bef9-bef2cbf0f0c2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_7e36622e-ffec-4aec-8ba1-9a9cf4c5f756" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b2fb77e2-4208-4d39-9f70-a32c17675828" xlink:to="loc_us-gaap_Revenues_7e36622e-ffec-4aec-8ba1-9a9cf4c5f756" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestChangeInRedemptionValue_e2860c7b-026d-4606-99ba-20f6fce74bc2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MinorityInterestChangeInRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b2fb77e2-4208-4d39-9f70-a32c17675828" xlink:to="loc_us-gaap_MinorityInterestChangeInRedemptionValue_e2860c7b-026d-4606-99ba-20f6fce74bc2" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/StockholdersEquityDetails" xlink:type="simple" xlink:href="iesc-20250331.xsd#StockholdersEquityDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/StockholdersEquityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_25860c06-7e22-4f49-8798-cef2f8aeedfb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_25860c06-7e22-4f49-8798-cef2f8aeedfb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramAxis_3493d674-840c-4f5d-9361-1ecd435b72de" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_25860c06-7e22-4f49-8798-cef2f8aeedfb" xlink:to="loc_srt_ShareRepurchaseProgramAxis_3493d674-840c-4f5d-9361-1ecd435b72de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_3493d674-840c-4f5d-9361-1ecd435b72de_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ShareRepurchaseProgramAxis_3493d674-840c-4f5d-9361-1ecd435b72de" xlink:to="loc_srt_ShareRepurchaseProgramDomain_3493d674-840c-4f5d-9361-1ecd435b72de_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_01181915-050d-4043-a4e6-8068bd80e4b0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ShareRepurchaseProgramAxis_3493d674-840c-4f5d-9361-1ecd435b72de" xlink:to="loc_srt_ShareRepurchaseProgramDomain_01181915-050d-4043-a4e6-8068bd80e4b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_EquityIncentivePlanMember_ea15d6c4-031b-4520-bf30-034eeee68ca4" xlink:href="iesc-20250331.xsd#iesc_EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_01181915-050d-4043-a4e6-8068bd80e4b0" xlink:to="loc_iesc_EquityIncentivePlanMember_ea15d6c4-031b-4520-bf30-034eeee68ca4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepurchaseAgreementsMember_1a306741-56d3-4a39-993f-58ead8e75b2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RepurchaseAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_01181915-050d-4043-a4e6-8068bd80e4b0" xlink:to="loc_us-gaap_RepurchaseAgreementsMember_1a306741-56d3-4a39-993f-58ead8e75b2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_AmendedEquityIncentivePlanMember_7eb06dbd-4905-429b-b576-95dbf403c66c" xlink:href="iesc-20250331.xsd#iesc_AmendedEquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_01181915-050d-4043-a4e6-8068bd80e4b0" xlink:to="loc_iesc_AmendedEquityIncentivePlanMember_7eb06dbd-4905-429b-b576-95dbf403c66c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_fe2efbb2-9210-4553-84ad-56abca6cc9c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_25860c06-7e22-4f49-8798-cef2f8aeedfb" xlink:to="loc_us-gaap_AwardTypeAxis_fe2efbb2-9210-4553-84ad-56abca6cc9c1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fe2efbb2-9210-4553-84ad-56abca6cc9c1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_fe2efbb2-9210-4553-84ad-56abca6cc9c1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fe2efbb2-9210-4553-84ad-56abca6cc9c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_04a3cb7e-43b8-41b9-b85f-f73df5f1608b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_fe2efbb2-9210-4553-84ad-56abca6cc9c1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_04a3cb7e-43b8-41b9-b85f-f73df5f1608b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_212653a7-6d72-4724-8917-07d2378d51e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_04a3cb7e-43b8-41b9-b85f-f73df5f1608b" xlink:to="loc_us-gaap_RestrictedStockMember_212653a7-6d72-4724-8917-07d2378d51e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PhantomShareUnitsPSUsMember_9530204d-133f-4de3-b728-908575be685f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PhantomShareUnitsPSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_04a3cb7e-43b8-41b9-b85f-f73df5f1608b" xlink:to="loc_us-gaap_PhantomShareUnitsPSUsMember_9530204d-133f-4de3-b728-908575be685f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_45c32459-3cd9-4991-84eb-fa0fb7a28951" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_04a3cb7e-43b8-41b9-b85f-f73df5f1608b" xlink:to="loc_us-gaap_PerformanceSharesMember_45c32459-3cd9-4991-84eb-fa0fb7a28951" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_PhantomShareUnitsEmployeePSUsMember_df25200e-728c-45a4-b932-3b1026030499" xlink:href="iesc-20250331.xsd#iesc_PhantomShareUnitsEmployeePSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_04a3cb7e-43b8-41b9-b85f-f73df5f1608b" xlink:to="loc_iesc_PhantomShareUnitsEmployeePSUsMember_df25200e-728c-45a4-b932-3b1026030499" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_5498f6bf-9292-44e3-af25-497b7856d870" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_04a3cb7e-43b8-41b9-b85f-f73df5f1608b" xlink:to="loc_us-gaap_EmployeeStockOptionMember_5498f6bf-9292-44e3-af25-497b7856d870" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_36b1fd79-8d9f-4760-a89d-297c8a4877cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_25860c06-7e22-4f49-8798-cef2f8aeedfb" xlink:to="loc_us-gaap_PlanNameAxis_36b1fd79-8d9f-4760-a89d-297c8a4877cf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_36b1fd79-8d9f-4760-a89d-297c8a4877cf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_36b1fd79-8d9f-4760-a89d-297c8a4877cf" xlink:to="loc_us-gaap_PlanNameDomain_36b1fd79-8d9f-4760-a89d-297c8a4877cf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_99d621c2-8ba6-4706-8273-a1a1c6159a4a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_36b1fd79-8d9f-4760-a89d-297c8a4877cf" xlink:to="loc_us-gaap_PlanNameDomain_99d621c2-8ba6-4706-8273-a1a1c6159a4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_2bddb3ed-da72-4dec-8159-d27134ca96ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_25860c06-7e22-4f49-8798-cef2f8aeedfb" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_2bddb3ed-da72-4dec-8159-d27134ca96ab" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_2bddb3ed-da72-4dec-8159-d27134ca96ab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_2bddb3ed-da72-4dec-8159-d27134ca96ab" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_2bddb3ed-da72-4dec-8159-d27134ca96ab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_5634c565-8796-4863-a879-60f293495412" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_2bddb3ed-da72-4dec-8159-d27134ca96ab" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_5634c565-8796-4863-a879-60f293495412" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_e8c5a4de-0f69-4371-9ed4-191fcb7e77c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_5634c565-8796-4863-a879-60f293495412" xlink:to="loc_us-gaap_SubsequentEventMember_e8c5a4de-0f69-4371-9ed4-191fcb7e77c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_e7ad4bac-9cfd-4502-96aa-04733f3ab9e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_e7ad4bac-9cfd-4502-96aa-04733f3ab9e8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_3bbe7346-81bf-42f9-90a9-7116d282089a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_3bbe7346-81bf-42f9-90a9-7116d282089a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_afed08c5-8d21-4ac7-bd82-1451f0847d56" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_afed08c5-8d21-4ac7-bd82-1451f0847d56" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_57deaa14-d9b3-4868-bec0-90fb53d5a752" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_57deaa14-d9b3-4868-bec0-90fb53d5a752" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_4b9c1e4a-ff7c-46b8-be7d-cb525020c4a2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_4b9c1e4a-ff7c-46b8-be7d-cb525020c4a2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_7ebe125a-ab26-46bf-9604-051de9743447" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_SharesIssued_7ebe125a-ab26-46bf-9604-051de9743447" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited_73014272-f307-47a7-a134-3f8f91a97286" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited_73014272-f307-47a7-a134-3f8f91a97286" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_f2c633fb-3e1d-4315-a4d3-b166d2b61d0b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_SharesOutstanding_f2c633fb-3e1d-4315-a4d3-b166d2b61d0b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockAcquiredAverageCostPerShare_560b4c4f-a7ec-4268-8e15-9a4722aff180" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockAcquiredAverageCostPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_TreasuryStockAcquiredAverageCostPerShare_560b4c4f-a7ec-4268-8e15-9a4722aff180" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_e5d550b1-2fb1-4b24-ae17-c103054f8f12" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_e5d550b1-2fb1-4b24-ae17-c103054f8f12" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StockRepurchaseProgramAuthorizedAmount1_adec036f-0a78-43ff-917f-7ac524b2faeb" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StockRepurchaseProgramAuthorizedAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_srt_StockRepurchaseProgramAuthorizedAmount1_adec036f-0a78-43ff-917f-7ac524b2faeb" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_3f763914-c4c2-4c04-b814-e0fc67ff8dd7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_3f763914-c4c2-4c04-b814-e0fc67ff8dd7" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_88d82dfb-c8fc-42df-ba23-37f73811fb50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_88d82dfb-c8fc-42df-ba23-37f73811fb50" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_90dbfa9a-6515-4395-b024-c0cf880d23d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_90dbfa9a-6515-4395-b024-c0cf880d23d2" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_995a6976-9d8a-4cfe-a9ee-72cbf8318b42" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_995a6976-9d8a-4cfe-a9ee-72cbf8318b42" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_09744ce0-34e5-4094-8e6e-e38ffe6e56e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_09744ce0-34e5-4094-8e6e-e38ffe6e56e6" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_7c7c8730-bfea-4de0-b7d3-58ecf7fe8c49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_7c7c8730-bfea-4de0-b7d3-58ecf7fe8c49" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_04431dca-39e7-4c5b-bb50-cf40cf91de2b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued_15c144cb-fb8d-4fdf-a00b-6ae199ca87d0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued_15c144cb-fb8d-4fdf-a00b-6ae199ca87d0" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_deb76a48-da2b-42f9-90d6-5c5f4e9f26e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7a706ede-4549-4764-8b1b-13ef16ba3ba8" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_deb76a48-da2b-42f9-90d6-5c5f4e9f26e5" xlink:type="arc" order="19"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/InvestmentsEquityMethodandJointVenturesDetails" xlink:type="simple" xlink:href="iesc-20250331.xsd#InvestmentsEquityMethodandJointVenturesDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/InvestmentsEquityMethodandJointVenturesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_18fc7c81-223e-4c85-af65-30f4dd494260" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_84bf4703-ada1-4858-941c-3be07a422782" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_18fc7c81-223e-4c85-af65-30f4dd494260" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_84bf4703-ada1-4858-941c-3be07a422782" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_9d7ee6c9-4747-47ed-8e6d-95a09f982e29" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_84bf4703-ada1-4858-941c-3be07a422782" xlink:to="loc_us-gaap_FinancialInstrumentAxis_9d7ee6c9-4747-47ed-8e6d-95a09f982e29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_9d7ee6c9-4747-47ed-8e6d-95a09f982e29_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_9d7ee6c9-4747-47ed-8e6d-95a09f982e29" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_9d7ee6c9-4747-47ed-8e6d-95a09f982e29_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0bb27ad8-c248-426f-a66f-4380c29abc68" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_9d7ee6c9-4747-47ed-8e6d-95a09f982e29" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0bb27ad8-c248-426f-a66f-4380c29abc68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_JettMember_d7c2bfc7-ca21-498b-973a-7d8883c59040" xlink:href="iesc-20250331.xsd#iesc_JettMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0bb27ad8-c248-426f-a66f-4380c29abc68" xlink:to="loc_iesc_JettMember_d7c2bfc7-ca21-498b-973a-7d8883c59040" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_5bc1a10b-abab-4374-90f6-c49e19190e12" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_84bf4703-ada1-4858-941c-3be07a422782" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_5bc1a10b-abab-4374-90f6-c49e19190e12" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_5bc1a10b-abab-4374-90f6-c49e19190e12_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_5bc1a10b-abab-4374-90f6-c49e19190e12" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_5bc1a10b-abab-4374-90f6-c49e19190e12_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_460a6a74-8a21-44c3-bc2f-37334eeed367" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_5bc1a10b-abab-4374-90f6-c49e19190e12" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_460a6a74-8a21-44c3-bc2f-37334eeed367" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_JettMember_a6601495-268f-4726-a2de-eb4d088c5285" xlink:href="iesc-20250331.xsd#iesc_JettMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_460a6a74-8a21-44c3-bc2f-37334eeed367" xlink:to="loc_iesc_JettMember_a6601495-268f-4726-a2de-eb4d088c5285" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_0e2750f7-21b5-4813-8406-fd4afaea331d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_84bf4703-ada1-4858-941c-3be07a422782" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_0e2750f7-21b5-4813-8406-fd4afaea331d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_0e2750f7-21b5-4813-8406-fd4afaea331d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_0e2750f7-21b5-4813-8406-fd4afaea331d" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_0e2750f7-21b5-4813-8406-fd4afaea331d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_9bb12ae3-9c81-4d30-a898-81fbe2f49fc9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_0e2750f7-21b5-4813-8406-fd4afaea331d" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_9bb12ae3-9c81-4d30-a898-81fbe2f49fc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_11ce8d28-5ce1-45f2-92a6-4df2a8b97420" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_84bf4703-ada1-4858-941c-3be07a422782" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_11ce8d28-5ce1-45f2-92a6-4df2a8b97420" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_11ce8d28-5ce1-45f2-92a6-4df2a8b97420_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_11ce8d28-5ce1-45f2-92a6-4df2a8b97420" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_11ce8d28-5ce1-45f2-92a6-4df2a8b97420_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_4b36a7be-c7ae-4912-80ce-cc9b2c3b0695" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_11ce8d28-5ce1-45f2-92a6-4df2a8b97420" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_4b36a7be-c7ae-4912-80ce-cc9b2c3b0695" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireInvestments_e3baf3ef-74bc-47c2-b9ca-42863b41b4da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_18fc7c81-223e-4c85-af65-30f4dd494260" xlink:to="loc_us-gaap_PaymentsToAcquireInvestments_e3baf3ef-74bc-47c2-b9ca-42863b41b4da" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_17f0183f-1880-47bc-9653-aed746d70e37" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_18fc7c81-223e-4c85-af65-30f4dd494260" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_17f0183f-1880-47bc-9653-aed746d70e37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_6fd556fe-30ef-4762-9fd5-381543e685fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_18fc7c81-223e-4c85-af65-30f4dd494260" xlink:to="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_6fd556fe-30ef-4762-9fd5-381543e685fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_974c5686-3951-4478-bd7d-f68c531b0180" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_18fc7c81-223e-4c85-af65-30f4dd494260" xlink:to="loc_us-gaap_EquityMethodInvestments_974c5686-3951-4478-bd7d-f68c531b0180" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_56547469-97f4-4db3-b237-3a2dde67470d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_18fc7c81-223e-4c85-af65-30f4dd494260" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_56547469-97f4-4db3-b237-3a2dde67470d" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/InvestmentsDebtandEquitySecuritiesDetails" xlink:type="simple" xlink:href="iesc-20250331.xsd#InvestmentsDebtandEquitySecuritiesDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/InvestmentsDebtandEquitySecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_5a654d87-8521-4293-9fa1-d5f10d24fcd8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_318168e9-80db-4c43-93b1-49fdbab60147" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_5a654d87-8521-4293-9fa1-d5f10d24fcd8" xlink:to="loc_us-gaap_MarketableSecuritiesTable_318168e9-80db-4c43-93b1-49fdbab60147" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_459c032d-7e11-4be4-948c-d93158dc5636" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_5a654d87-8521-4293-9fa1-d5f10d24fcd8" xlink:to="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_459c032d-7e11-4be4-948c-d93158dc5636" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradingSecuritiesDebt_f7794ec5-8377-43cf-84eb-99f81e91f758" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TradingSecuritiesDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_5a654d87-8521-4293-9fa1-d5f10d24fcd8" xlink:to="loc_us-gaap_TradingSecuritiesDebt_f7794ec5-8377-43cf-84eb-99f81e91f758" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesCurrent_330295a9-6220-4a94-b769-7b57748bad19" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MarketableSecuritiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_5a654d87-8521-4293-9fa1-d5f10d24fcd8" xlink:to="loc_us-gaap_MarketableSecuritiesCurrent_330295a9-6220-4a94-b769-7b57748bad19" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/FairValueMeasurementsDetails" xlink:type="simple" xlink:href="iesc-20250331.xsd#FairValueMeasurementsDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/FairValueMeasurementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a6ac17c3-cab3-4324-bd59-a12483ca7da0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a6ac17c3-cab3-4324-bd59-a12483ca7da0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_83e857b5-7a61-4afe-a754-3988d71ec346" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a6ac17c3-cab3-4324-bd59-a12483ca7da0" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_83e857b5-7a61-4afe-a754-3988d71ec346" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_83e857b5-7a61-4afe-a754-3988d71ec346_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_83e857b5-7a61-4afe-a754-3988d71ec346" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_83e857b5-7a61-4afe-a754-3988d71ec346_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1d3a8da2-e8fa-4dd6-9741-a8c9aae145ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_83e857b5-7a61-4afe-a754-3988d71ec346" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1d3a8da2-e8fa-4dd6-9741-a8c9aae145ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_c0feba50-6150-4e7c-a1d0-da04815b20ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1d3a8da2-e8fa-4dd6-9741-a8c9aae145ea" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_c0feba50-6150-4e7c-a1d0-da04815b20ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_1fb79acf-ba2a-4119-9550-e0855d9937ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1d3a8da2-e8fa-4dd6-9741-a8c9aae145ea" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_1fb79acf-ba2a-4119-9550-e0855d9937ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_08635dd4-16fa-49b6-a870-d81b15a0a7b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a6ac17c3-cab3-4324-bd59-a12483ca7da0" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_08635dd4-16fa-49b6-a870-d81b15a0a7b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_08635dd4-16fa-49b6-a870-d81b15a0a7b6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_08635dd4-16fa-49b6-a870-d81b15a0a7b6" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_08635dd4-16fa-49b6-a870-d81b15a0a7b6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_483ae380-38f5-4f1d-bbbf-2e15b4ce5097" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_08635dd4-16fa-49b6-a870-d81b15a0a7b6" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_483ae380-38f5-4f1d-bbbf-2e15b4ce5097" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_8cdeb9ba-e9a2-44a8-be1d-80ec8a35c3e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_483ae380-38f5-4f1d-bbbf-2e15b4ce5097" xlink:to="loc_us-gaap_EquitySecuritiesMember_8cdeb9ba-e9a2-44a8-be1d-80ec8a35c3e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_880875d0-c8e9-453f-9bf8-70f9fc871f2f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a6ac17c3-cab3-4324-bd59-a12483ca7da0" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_880875d0-c8e9-453f-9bf8-70f9fc871f2f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_880875d0-c8e9-453f-9bf8-70f9fc871f2f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_880875d0-c8e9-453f-9bf8-70f9fc871f2f" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_880875d0-c8e9-453f-9bf8-70f9fc871f2f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_fb34c5d6-5512-4c6d-8a81-bca39f67511b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_880875d0-c8e9-453f-9bf8-70f9fc871f2f" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_fb34c5d6-5512-4c6d-8a81-bca39f67511b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsMember_7810838f-aff1-4651-8467-b760dd2b7f48" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_fb34c5d6-5512-4c6d-8a81-bca39f67511b" xlink:to="loc_us-gaap_CommitmentsMember_7810838f-aff1-4651-8467-b760dd2b7f48" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_cd1f6c3d-b940-4c2a-b009-b51d0e9113b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_fb34c5d6-5512-4c6d-8a81-bca39f67511b" xlink:to="loc_us-gaap_EquitySecuritiesMember_cd1f6c3d-b940-4c2a-b009-b51d0e9113b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_65d426f9-3603-4e59-a2a7-632899f74ec5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_65d426f9-3603-4e59-a2a7-632899f74ec5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_6388a929-dbbc-47c0-b8a5-b176977f6434" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_6388a929-dbbc-47c0-b8a5-b176977f6434" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradingSecuritiesDebt_56e51d50-0687-464c-9eed-e7569c748db9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TradingSecuritiesDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_TradingSecuritiesDebt_56e51d50-0687-464c-9eed-e7569c748db9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFVNINoncurrent_6966c604-72a7-4166-a3f5-8ea51f92f0f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesFVNINoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_EquitySecuritiesFVNINoncurrent_6966c604-72a7-4166-a3f5-8ea51f92f0f9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_b67b4264-a631-4c54-8905-1155d69c97c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_b67b4264-a631-4c54-8905-1155d69c97c2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_7d8fc4b9-b80e-4cd3-aeb0-1e56993691a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_7d8fc4b9-b80e-4cd3-aeb0-1e56993691a7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetAssetLiability_27b59b55-5362-4a81-831d-f81057d78a71" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueNetAssetLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_FairValueNetAssetLiability_27b59b55-5362-4a81-831d-f81057d78a71" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_1384a615-5158-4db7-908b-4109ef8f4cdf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_1384a615-5158-4db7-908b-4109ef8f4cdf" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueRecurringBasisUnobservableInputReconciliationLiabilityGainLossStatementOfIncomeExtensibleList_1acd9307-adeb-42d0-8f20-a4b5a0363990" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueRecurringBasisUnobservableInputReconciliationLiabilityGainLossStatementOfIncomeExtensibleList"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_FairValueRecurringBasisUnobservableInputReconciliationLiabilityGainLossStatementOfIncomeExtensibleList_1acd9307-adeb-42d0-8f20-a4b5a0363990" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements_b6f718d7-ed98-417c-b000-fbdbbd49bc3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements_b6f718d7-ed98-417c-b000-fbdbbd49bc3e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases_451598df-e3c7-4465-99b7-800d23daae9d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases_451598df-e3c7-4465-99b7-800d23daae9d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNi_62f7260b-d4ad-40d5-8704-11bbf6346152" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesFvNi"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_EquitySecuritiesFvNi_62f7260b-d4ad-40d5-8704-11bbf6346152" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss_60ebde15-229b-4694-90e8-5bdde6a87194" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss_60ebde15-229b-4694-90e8-5bdde6a87194" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesTradingUnrealizedGainLoss_9003156b-c97d-4319-a670-391a9a5cc24e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesTradingUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_DebtSecuritiesTradingUnrealizedGainLoss_9003156b-c97d-4319-a670-391a9a5cc24e" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss_7de96905-6329-4a7b-abf2-5cad76fe1cd9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss_7de96905-6329-4a7b-abf2-5cad76fe1cd9" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_e2b9fce0-3787-4e8c-b3a5-135b6f2a2946" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_e2b9fce0-3787-4e8c-b3a5-135b6f2a2946" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_5eba5faa-6cc8-4bde-ae7d-8bb620deebe5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_5eba5faa-6cc8-4bde-ae7d-8bb620deebe5" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_bc236601-9bc0-4bdc-9dc7-592a182bb087" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_bc236601-9bc0-4bdc-9dc7-592a182bb087" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueRecurringBasisUnobservableInputReconciliationAssetGainLossStatementOfIncomeExtensibleList_f8d8454d-d375-494c-bf0a-5679e2e134af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueRecurringBasisUnobservableInputReconciliationAssetGainLossStatementOfIncomeExtensibleList"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_FairValueRecurringBasisUnobservableInputReconciliationAssetGainLossStatementOfIncomeExtensibleList_f8d8454d-d375-494c-bf0a-5679e2e134af" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_cd95c34a-28d0-4553-91f3-d831fb067a25" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_cd95c34a-28d0-4553-91f3-d831fb067a25" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireInvestments_5ea70f48-0474-49b6-8a85-34bc5e4d5c74" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6219a3c0-172b-41b1-8298-eec70c5d1639" xlink:to="loc_us-gaap_PaymentsToAcquireInvestments_5ea70f48-0474-49b6-8a85-34bc5e4d5c74" xlink:type="arc" order="20"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/GoodwillandIntangibleAssetsGoodwillDetails" xlink:type="simple" xlink:href="iesc-20250331.xsd#GoodwillandIntangibleAssetsGoodwillDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/GoodwillandIntangibleAssetsGoodwillDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_26b657b1-ca6d-4596-b76c-d63d7c67d6b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_0876fefd-d878-426b-9efb-67ca6c1ae4a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_26b657b1-ca6d-4596-b76c-d63d7c67d6b3" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_0876fefd-d878-426b-9efb-67ca6c1ae4a6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_505c8d7e-413a-49c1-830a-6ddfb99e241f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_0876fefd-d878-426b-9efb-67ca6c1ae4a6" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_505c8d7e-413a-49c1-830a-6ddfb99e241f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_505c8d7e-413a-49c1-830a-6ddfb99e241f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_505c8d7e-413a-49c1-830a-6ddfb99e241f" xlink:to="loc_us-gaap_SegmentDomain_505c8d7e-413a-49c1-830a-6ddfb99e241f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_dacd88b0-ec64-4e48-a731-da75b48e0d5c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_505c8d7e-413a-49c1-830a-6ddfb99e241f" xlink:to="loc_us-gaap_SegmentDomain_dacd88b0-ec64-4e48-a731-da75b48e0d5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_CommercialandIndustrialMember_cc00281e-6ec0-4d50-936a-ff34081afe5a" xlink:href="iesc-20250331.xsd#iesc_CommercialandIndustrialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_dacd88b0-ec64-4e48-a731-da75b48e0d5c" xlink:to="loc_iesc_CommercialandIndustrialMember_cc00281e-6ec0-4d50-936a-ff34081afe5a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_ResidentialMember_74557a4f-e651-4869-9629-9750dddb4f99" xlink:href="iesc-20250331.xsd#iesc_ResidentialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_dacd88b0-ec64-4e48-a731-da75b48e0d5c" xlink:to="loc_iesc_ResidentialMember_74557a4f-e651-4869-9629-9750dddb4f99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_InfrastructureSolutionsMember_347c5d4a-b163-4ee9-9179-fb274bfe4c93" xlink:href="iesc-20250331.xsd#iesc_InfrastructureSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_dacd88b0-ec64-4e48-a731-da75b48e0d5c" xlink:to="loc_iesc_InfrastructureSolutionsMember_347c5d4a-b163-4ee9-9179-fb274bfe4c93" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_CommunicationsMember_85fab88c-7ad0-49a0-a076-5d8169da94b2" xlink:href="iesc-20250331.xsd#iesc_CommunicationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_dacd88b0-ec64-4e48-a731-da75b48e0d5c" xlink:to="loc_iesc_CommunicationsMember_85fab88c-7ad0-49a0-a076-5d8169da94b2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_69c58d0c-6a83-4e1d-b193-2ecdca8cbd4b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_0876fefd-d878-426b-9efb-67ca6c1ae4a6" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_69c58d0c-6a83-4e1d-b193-2ecdca8cbd4b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_69c58d0c-6a83-4e1d-b193-2ecdca8cbd4b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_69c58d0c-6a83-4e1d-b193-2ecdca8cbd4b" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_69c58d0c-6a83-4e1d-b193-2ecdca8cbd4b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_9519fbf6-9f31-4e98-b4da-2996482e1bdb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_69c58d0c-6a83-4e1d-b193-2ecdca8cbd4b" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_9519fbf6-9f31-4e98-b4da-2996482e1bdb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_ArrowEngineCompanyMember_a4a60b42-86c0-4f92-a698-1389a5794d0e" xlink:href="iesc-20250331.xsd#iesc_ArrowEngineCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_9519fbf6-9f31-4e98-b4da-2996482e1bdb" xlink:to="loc_iesc_ArrowEngineCompanyMember_a4a60b42-86c0-4f92-a698-1389a5794d0e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_6f62445c-472b-4147-b26a-c88df366f6f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_26b657b1-ca6d-4596-b76c-d63d7c67d6b3" xlink:to="loc_us-gaap_Goodwill_6f62445c-472b-4147-b26a-c88df366f6f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_bf51034c-7d0b-40fb-9e6d-8d0649ee2eea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillPeriodIncreaseDecrease_7e505d38-d210-4787-9b21-070dd3eb7642" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillPeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_26b657b1-ca6d-4596-b76c-d63d7c67d6b3" xlink:to="loc_us-gaap_GoodwillPeriodIncreaseDecrease_7e505d38-d210-4787-9b21-070dd3eb7642" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillWrittenOffRelatedToSaleOfBusinessUnit_be0d145a-7fcc-47a1-ba5e-feeed47dc2bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillWrittenOffRelatedToSaleOfBusinessUnit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_26b657b1-ca6d-4596-b76c-d63d7c67d6b3" xlink:to="loc_us-gaap_GoodwillWrittenOffRelatedToSaleOfBusinessUnit_be0d145a-7fcc-47a1-ba5e-feeed47dc2bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAcquiredDuringPeriod_16e75962-fd62-424d-8eb8-89fb81184418" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillAcquiredDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_26b657b1-ca6d-4596-b76c-d63d7c67d6b3" xlink:to="loc_us-gaap_GoodwillAcquiredDuringPeriod_16e75962-fd62-424d-8eb8-89fb81184418" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_69e9d62f-ddab-42d7-96ea-ce584f17d964" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_26b657b1-ca6d-4596-b76c-d63d7c67d6b3" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_69e9d62f-ddab-42d7-96ea-ce584f17d964" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_638fee04-03ee-4600-a41d-29b828275ad2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_26b657b1-ca6d-4596-b76c-d63d7c67d6b3" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_638fee04-03ee-4600-a41d-29b828275ad2" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/GoodwillandIntangibleAssetsIntangiblesDetails" xlink:type="simple" xlink:href="iesc-20250331.xsd#GoodwillandIntangibleAssetsIntangiblesDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/GoodwillandIntangibleAssetsIntangiblesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_c943584c-4d09-40ad-8771-1a48c276c0f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_65b7adf2-98b2-41b1-9ae3-a7b5800fb704" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_c943584c-4d09-40ad-8771-1a48c276c0f6" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_65b7adf2-98b2-41b1-9ae3-a7b5800fb704" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3b728a43-693a-41f4-8b77-b4233b36b3ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_65b7adf2-98b2-41b1-9ae3-a7b5800fb704" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3b728a43-693a-41f4-8b77-b4233b36b3ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3b728a43-693a-41f4-8b77-b4233b36b3ac_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3b728a43-693a-41f4-8b77-b4233b36b3ac" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3b728a43-693a-41f4-8b77-b4233b36b3ac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_8fe39e5c-4212-4b29-917d-97cf041341b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_3b728a43-693a-41f4-8b77-b4233b36b3ac" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_8fe39e5c-4212-4b29-917d-97cf041341b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksAndTradeNamesMember_6a6ee6ef-ab6a-4ef0-92cd-7b6de5e63eb8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TrademarksAndTradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_8fe39e5c-4212-4b29-917d-97cf041341b3" xlink:to="loc_us-gaap_TrademarksAndTradeNamesMember_6a6ee6ef-ab6a-4ef0-92cd-7b6de5e63eb8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_1df5de57-dc3f-4ece-a343-6a7b9b598559" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_8fe39e5c-4212-4b29-917d-97cf041341b3" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_1df5de57-dc3f-4ece-a343-6a7b9b598559" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_30e21265-d4cb-4b03-a0c1-35bf22bddaec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_8fe39e5c-4212-4b29-917d-97cf041341b3" xlink:to="loc_us-gaap_CustomerRelationshipsMember_30e21265-d4cb-4b03-a0c1-35bf22bddaec" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_afecdb54-d988-4cc5-a6f8-07e61defe775" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncompeteAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_8fe39e5c-4212-4b29-917d-97cf041341b3" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_afecdb54-d988-4cc5-a6f8-07e61defe775" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OrderOrProductionBacklogMember_07dbc4fb-56d1-4611-b9cb-5a126d9dfdcd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OrderOrProductionBacklogMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_8fe39e5c-4212-4b29-917d-97cf041341b3" xlink:to="loc_us-gaap_OrderOrProductionBacklogMember_07dbc4fb-56d1-4611-b9cb-5a126d9dfdcd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_959576c7-d391-405e-ab7d-c79ae7b86241" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_65b7adf2-98b2-41b1-9ae3-a7b5800fb704" xlink:to="loc_srt_RangeAxis_959576c7-d391-405e-ab7d-c79ae7b86241" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_959576c7-d391-405e-ab7d-c79ae7b86241_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_959576c7-d391-405e-ab7d-c79ae7b86241" xlink:to="loc_srt_RangeMember_959576c7-d391-405e-ab7d-c79ae7b86241_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_29d115a0-01e7-49d9-a59b-14964a87b97b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_959576c7-d391-405e-ab7d-c79ae7b86241" xlink:to="loc_srt_RangeMember_29d115a0-01e7-49d9-a59b-14964a87b97b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_6b82694b-7176-444d-8276-22cb4f5e3540" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_29d115a0-01e7-49d9-a59b-14964a87b97b" xlink:to="loc_srt_MinimumMember_6b82694b-7176-444d-8276-22cb4f5e3540" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_46898260-eee9-4c1b-ad54-fd94243768c9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_29d115a0-01e7-49d9-a59b-14964a87b97b" xlink:to="loc_srt_MaximumMember_46898260-eee9-4c1b-ad54-fd94243768c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_b97803aa-d45e-442d-9233-261ce7cfaa46" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_c943584c-4d09-40ad-8771-1a48c276c0f6" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_b97803aa-d45e-442d-9233-261ce7cfaa46" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_e3c8eef5-b1be-4db3-b813-7d896bf8850d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_c943584c-4d09-40ad-8771-1a48c276c0f6" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_e3c8eef5-b1be-4db3-b813-7d896bf8850d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_1e56d97e-55ab-48b8-b9d5-665c8b2e9f3a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_c943584c-4d09-40ad-8771-1a48c276c0f6" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_1e56d97e-55ab-48b8-b9d5-665c8b2e9f3a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_56cb4407-646e-4032-a16b-8d5c5253d14e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_c943584c-4d09-40ad-8771-1a48c276c0f6" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_56cb4407-646e-4032-a16b-8d5c5253d14e" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="iesc-20250331.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/CommitmentsandContingenciesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_b8601585-6ba7-4ada-9f27-1d6e51ebb970" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_2886b819-a486-4289-81f4-807706176276" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_b8601585-6ba7-4ada-9f27-1d6e51ebb970" xlink:to="loc_us-gaap_LossContingenciesTable_2886b819-a486-4289-81f4-807706176276" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_1ae74eb8-e6a2-407d-b7c7-da88d63c90f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_2886b819-a486-4289-81f4-807706176276" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_1ae74eb8-e6a2-407d-b7c7-da88d63c90f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_1ae74eb8-e6a2-407d-b7c7-da88d63c90f8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_1ae74eb8-e6a2-407d-b7c7-da88d63c90f8" xlink:to="loc_us-gaap_LossContingencyNatureDomain_1ae74eb8-e6a2-407d-b7c7-da88d63c90f8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_248f0d54-9592-4746-bc96-a27308c24837" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_1ae74eb8-e6a2-407d-b7c7-da88d63c90f8" xlink:to="loc_us-gaap_LossContingencyNatureDomain_248f0d54-9592-4746-bc96-a27308c24837" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_InsuranceRelatedMember_a82b151e-c0ad-4df2-9fc3-3fcf4180580c" xlink:href="iesc-20250331.xsd#iesc_InsuranceRelatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_248f0d54-9592-4746-bc96-a27308c24837" xlink:to="loc_iesc_InsuranceRelatedMember_a82b151e-c0ad-4df2-9fc3-3fcf4180580c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_58d10238-3f95-4d03-9244-c2fc8dbe07d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_b8601585-6ba7-4ada-9f27-1d6e51ebb970" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_58d10238-3f95-4d03-9244-c2fc8dbe07d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualAtCarryingValue_1a9c82e3-7cfd-479d-bc35-48735db31e6d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyAccrualAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_b8601585-6ba7-4ada-9f27-1d6e51ebb970" xlink:to="loc_us-gaap_LossContingencyAccrualAtCarryingValue_1a9c82e3-7cfd-479d-bc35-48735db31e6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractsReceivableClaimsAndUncertainAmounts_465d40dd-10af-4147-ad81-b40ca59af9f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractsReceivableClaimsAndUncertainAmounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_b8601585-6ba7-4ada-9f27-1d6e51ebb970" xlink:to="loc_us-gaap_ContractsReceivableClaimsAndUncertainAmounts_465d40dd-10af-4147-ad81-b40ca59af9f1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleAndCollectionOfReceivables_2cf0bdc4-a7e5-4ba8-82d7-4ecc58151915" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromSaleAndCollectionOfReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_b8601585-6ba7-4ada-9f27-1d6e51ebb970" xlink:to="loc_us-gaap_ProceedsFromSaleAndCollectionOfReceivables_2cf0bdc4-a7e5-4ba8-82d7-4ecc58151915" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_0908705f-05c6-4b93-a3c2-9a257273069b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_b8601585-6ba7-4ada-9f27-1d6e51ebb970" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_0908705f-05c6-4b93-a3c2-9a257273069b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_Estimatedcostofcompletionofbondedproject_c54917de-eefe-41dd-9d3b-65eed07ef75a" xlink:href="iesc-20250331.xsd#iesc_Estimatedcostofcompletionofbondedproject"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_b8601585-6ba7-4ada-9f27-1d6e51ebb970" xlink:to="loc_iesc_Estimatedcostofcompletionofbondedproject_c54917de-eefe-41dd-9d3b-65eed07ef75a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyReceivable_1a8c78c5-b245-4b56-9eaf-678a448d6b5e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_b8601585-6ba7-4ada-9f27-1d6e51ebb970" xlink:to="loc_us-gaap_LossContingencyReceivable_1a8c78c5-b245-4b56-9eaf-678a448d6b5e" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="iesc-20250331.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_5a198292-f468-4052-9eaf-5202e4e33e8a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_f1a156f3-b1ff-4eef-9164-ec839179cf8e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_5a198292-f468-4052-9eaf-5202e4e33e8a" xlink:to="loc_us-gaap_SubsequentEventTable_f1a156f3-b1ff-4eef-9164-ec839179cf8e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_783df264-6865-4443-9723-495b7d07d66c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_f1a156f3-b1ff-4eef-9164-ec839179cf8e" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_783df264-6865-4443-9723-495b7d07d66c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_783df264-6865-4443-9723-495b7d07d66c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_783df264-6865-4443-9723-495b7d07d66c" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_783df264-6865-4443-9723-495b7d07d66c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_7b693079-f358-43e9-907c-ddb47176d5d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_783df264-6865-4443-9723-495b7d07d66c" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_7b693079-f358-43e9-907c-ddb47176d5d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_16f73c11-f56d-45ac-9348-ef3879fad68a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_7b693079-f358-43e9-907c-ddb47176d5d3" xlink:to="loc_us-gaap_SubsequentEventMember_16f73c11-f56d-45ac-9348-ef3879fad68a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_d7ee4473-70b1-4493-bf60-3238dfecaa97" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_f1a156f3-b1ff-4eef-9164-ec839179cf8e" xlink:to="loc_us-gaap_VariableRateAxis_d7ee4473-70b1-4493-bf60-3238dfecaa97" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_d7ee4473-70b1-4493-bf60-3238dfecaa97_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_d7ee4473-70b1-4493-bf60-3238dfecaa97" xlink:to="loc_us-gaap_VariableRateDomain_d7ee4473-70b1-4493-bf60-3238dfecaa97_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_74131d6d-b62c-4d03-b5cb-dc42cedcea9a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_d7ee4473-70b1-4493-bf60-3238dfecaa97" xlink:to="loc_us-gaap_VariableRateDomain_74131d6d-b62c-4d03-b5cb-dc42cedcea9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_50b10d66-4c7c-4d3d-9116-7026ee28b2c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_74131d6d-b62c-4d03-b5cb-dc42cedcea9a" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_50b10d66-4c7c-4d3d-9116-7026ee28b2c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_b9ef74c1-e922-4ca7-ae97-fe2accf44864" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_74131d6d-b62c-4d03-b5cb-dc42cedcea9a" xlink:to="loc_us-gaap_BaseRateMember_b9ef74c1-e922-4ca7-ae97-fe2accf44864" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_ae552f0e-0779-4809-9410-f2ddbca16c0e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_f1a156f3-b1ff-4eef-9164-ec839179cf8e" xlink:to="loc_srt_RangeAxis_ae552f0e-0779-4809-9410-f2ddbca16c0e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_ae552f0e-0779-4809-9410-f2ddbca16c0e_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_ae552f0e-0779-4809-9410-f2ddbca16c0e" xlink:to="loc_srt_RangeMember_ae552f0e-0779-4809-9410-f2ddbca16c0e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_00e6bb45-84e0-448d-9fa6-90d9e8f05547" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_ae552f0e-0779-4809-9410-f2ddbca16c0e" xlink:to="loc_srt_RangeMember_00e6bb45-84e0-448d-9fa6-90d9e8f05547" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_73dcb0b1-28de-4ce6-894a-a3c98b572858" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_00e6bb45-84e0-448d-9fa6-90d9e8f05547" xlink:to="loc_srt_MinimumMember_73dcb0b1-28de-4ce6-894a-a3c98b572858" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_5061a458-e262-4b98-9960-016ba58c4df8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_00e6bb45-84e0-448d-9fa6-90d9e8f05547" xlink:to="loc_srt_MaximumMember_5061a458-e262-4b98-9960-016ba58c4df8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_PricingLevelAxis_6acb9edb-ca22-4d58-b0ee-40fdbd5d790e" xlink:href="iesc-20250331.xsd#iesc_PricingLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_f1a156f3-b1ff-4eef-9164-ec839179cf8e" xlink:to="loc_iesc_PricingLevelAxis_6acb9edb-ca22-4d58-b0ee-40fdbd5d790e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_PricingLevelDomain_6acb9edb-ca22-4d58-b0ee-40fdbd5d790e_default" xlink:href="iesc-20250331.xsd#iesc_PricingLevelDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_iesc_PricingLevelAxis_6acb9edb-ca22-4d58-b0ee-40fdbd5d790e" xlink:to="loc_iesc_PricingLevelDomain_6acb9edb-ca22-4d58-b0ee-40fdbd5d790e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_PricingLevelDomain_5839eee6-e172-4596-9f45-822cc9a225e3" xlink:href="iesc-20250331.xsd#iesc_PricingLevelDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_iesc_PricingLevelAxis_6acb9edb-ca22-4d58-b0ee-40fdbd5d790e" xlink:to="loc_iesc_PricingLevelDomain_5839eee6-e172-4596-9f45-822cc9a225e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_PricingLevelIVMember_6e1cd9f5-4c38-4d1e-b928-df308230a329" xlink:href="iesc-20250331.xsd#iesc_PricingLevelIVMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_iesc_PricingLevelDomain_5839eee6-e172-4596-9f45-822cc9a225e3" xlink:to="loc_iesc_PricingLevelIVMember_6e1cd9f5-4c38-4d1e-b928-df308230a329" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_PricingLevelIIIMember_a497c6e4-35f8-4609-9027-9d35ca3b4fd1" xlink:href="iesc-20250331.xsd#iesc_PricingLevelIIIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_iesc_PricingLevelDomain_5839eee6-e172-4596-9f45-822cc9a225e3" xlink:to="loc_iesc_PricingLevelIIIMember_a497c6e4-35f8-4609-9027-9d35ca3b4fd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_PricingLevelIIMember_d65a8917-e277-440b-8f45-ce15748a7d46" xlink:href="iesc-20250331.xsd#iesc_PricingLevelIIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_iesc_PricingLevelDomain_5839eee6-e172-4596-9f45-822cc9a225e3" xlink:to="loc_iesc_PricingLevelIIMember_d65a8917-e277-440b-8f45-ce15748a7d46" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_PricingLevelIMember_332fc5d8-0f51-444c-9bfa-ebf084aa2578" xlink:href="iesc-20250331.xsd#iesc_PricingLevelIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_iesc_PricingLevelDomain_5839eee6-e172-4596-9f45-822cc9a225e3" xlink:to="loc_iesc_PricingLevelIMember_332fc5d8-0f51-444c-9bfa-ebf084aa2578" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_1fe44207-6898-4643-8182-d61e57f908d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_5a198292-f468-4052-9eaf-5202e4e33e8a" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_1fe44207-6898-4643-8182-d61e57f908d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_ConsolidatedTotalLeverageRatio_180a0994-1991-42e2-8ccc-637717defafa" xlink:href="iesc-20250331.xsd#iesc_ConsolidatedTotalLeverageRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_5a198292-f468-4052-9eaf-5202e4e33e8a" xlink:to="loc_iesc_ConsolidatedTotalLeverageRatio_180a0994-1991-42e2-8ccc-637717defafa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_CreditAgreementInterestMarginRate_47612c6f-c7dc-44c4-87f2-6b39e6e8d7ee" xlink:href="iesc-20250331.xsd#iesc_CreditAgreementInterestMarginRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_5a198292-f468-4052-9eaf-5202e4e33e8a" xlink:to="loc_iesc_CreditAgreementInterestMarginRate_47612c6f-c7dc-44c4-87f2-6b39e6e8d7ee" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/BusinessCombinationsandAssetAcquisitionsDetails" xlink:type="simple" xlink:href="iesc-20250331.xsd#BusinessCombinationsandAssetAcquisitionsDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/BusinessCombinationsandAssetAcquisitionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_00d26da3-f938-4948-8d0f-80e3249ffa66" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_fbe2677b-6268-4d86-a566-12fac6e9087a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_00d26da3-f938-4948-8d0f-80e3249ffa66" xlink:to="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_fbe2677b-6268-4d86-a566-12fac6e9087a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecurringAdjustmentAxis_a0e804b2-70c1-44f6-9271-1609dca1cd8b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonrecurringAdjustmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_fbe2677b-6268-4d86-a566-12fac6e9087a" xlink:to="loc_us-gaap_NonrecurringAdjustmentAxis_a0e804b2-70c1-44f6-9271-1609dca1cd8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecurringAdjustmentDomain_a0e804b2-70c1-44f6-9271-1609dca1cd8b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonrecurringAdjustmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_NonrecurringAdjustmentAxis_a0e804b2-70c1-44f6-9271-1609dca1cd8b" xlink:to="loc_us-gaap_NonrecurringAdjustmentDomain_a0e804b2-70c1-44f6-9271-1609dca1cd8b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecurringAdjustmentDomain_8933bc96-64b6-41ef-930b-396400e01a8f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonrecurringAdjustmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_NonrecurringAdjustmentAxis_a0e804b2-70c1-44f6-9271-1609dca1cd8b" xlink:to="loc_us-gaap_NonrecurringAdjustmentDomain_8933bc96-64b6-41ef-930b-396400e01a8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_bc57d2a5-60cd-42f8-ba3d-8dc908532b4e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionsProFormaRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_00d26da3-f938-4948-8d0f-80e3249ffa66" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_bc57d2a5-60cd-42f8-ba3d-8dc908532b4e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_dddd3997-99b1-4623-882e-8a56e2feea88" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_dddd3997-99b1-4623-882e-8a56e2feea88" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_5c45397d-7cb7-4ae2-b8fb-85b7747b9cba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_dddd3997-99b1-4623-882e-8a56e2feea88" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_5c45397d-7cb7-4ae2-b8fb-85b7747b9cba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_5c45397d-7cb7-4ae2-b8fb-85b7747b9cba_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_5c45397d-7cb7-4ae2-b8fb-85b7747b9cba" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_5c45397d-7cb7-4ae2-b8fb-85b7747b9cba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_70dd18c1-dce4-471a-b063-a5f74ece8ef4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_5c45397d-7cb7-4ae2-b8fb-85b7747b9cba" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_70dd18c1-dce4-471a-b063-a5f74ece8ef4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_ArrowEngineCompanyMember_016d988a-5dba-4977-866c-3770c6ce5896" xlink:href="iesc-20250331.xsd#iesc_ArrowEngineCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_70dd18c1-dce4-471a-b063-a5f74ece8ef4" xlink:to="loc_iesc_ArrowEngineCompanyMember_016d988a-5dba-4977-866c-3770c6ce5896" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_429cb199-42ed-451b-a51a-4841f1fef949" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:to="loc_us-gaap_Goodwill_429cb199-42ed-451b-a51a-4841f1fef949" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities_b29d5509-a674-46d4-a90f-713f1eef9f8d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities_b29d5509-a674-46d4-a90f-713f1eef9f8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_de030cc7-a4e0-43e8-bd2a-47133e25eeab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_de030cc7-a4e0-43e8-bd2a-47133e25eeab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_328cd8c4-3afc-466a-8e22-14b351c0295e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_328cd8c4-3afc-466a-8e22-14b351c0295e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssets_fb0e0949-9042-4eb9-b44a-e59f71cba89a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssets_fb0e0949-9042-4eb9-b44a-e59f71cba89a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_7971665f-8e61-4065-a1d8-7e11efcc21cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_7971665f-8e61-4065-a1d8-7e11efcc21cc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_c681bb16-3470-4745-84ac-48788a63f102" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_c681bb16-3470-4745-84ac-48788a63f102" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_d7b1540b-d228-4065-9aaf-e8a9189595bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_d7b1540b-d228-4065-9aaf-e8a9189595bf" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfBusinessesAcquired_c27ddeb0-1241-4477-be7b-7fb98400f4eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NumberOfBusinessesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:to="loc_us-gaap_NumberOfBusinessesAcquired_c27ddeb0-1241-4477-be7b-7fb98400f4eb" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_ac10bff2-fcb3-4d5e-8139-910410e304e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_ac10bff2-fcb3-4d5e-8139-910410e304e3" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAcquiredDuringPeriod_2804227a-1987-4fb8-a3c1-1878063e5541" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillAcquiredDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:to="loc_us-gaap_GoodwillAcquiredDuringPeriod_2804227a-1987-4fb8-a3c1-1878063e5541" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_2f41dfff-22e1-410d-97c9-bacae77c5ef1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:to="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_2f41dfff-22e1-410d-97c9-bacae77c5ef1" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_836aacc5-058c-43bc-bb16-8a55fd0c1107" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_836aacc5-058c-43bc-bb16-8a55fd0c1107" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases_a4318237-5eea-43c3-ab45-c32b0a3c213d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_a5990649-139e-43b6-854d-e0c14b568051" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases_a4318237-5eea-43c3-ab45-c32b0a3c213d" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_91c843d6-27e0-43d9-b0e3-b129d8e1262f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTable_11ad7ba7-37c7-4a79-8055-7397e3475ba0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_91c843d6-27e0-43d9-b0e3-b129d8e1262f" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTable_11ad7ba7-37c7-4a79-8055-7397e3475ba0" xlink:type="arc" order="3" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_3c72c607-c852-4054-9fc6-c11eafcd5bab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTable_11ad7ba7-37c7-4a79-8055-7397e3475ba0" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_3c72c607-c852-4054-9fc6-c11eafcd5bab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3c72c607-c852-4054-9fc6-c11eafcd5bab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d9f16433-22dd-495c-a53a-7b22952e1561" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_ArrowEngineCompanyMember_a28ae07f-4127-4219-b388-3962d45df67e" xlink:href="iesc-20250331.xsd#iesc_ArrowEngineCompanyMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_5348e0b1-fbb0-42f6-a2ca-d132391efd72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_91c843d6-27e0-43d9-b0e3-b129d8e1262f" xlink:to="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_5348e0b1-fbb0-42f6-a2ca-d132391efd72" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ies-co.com/role/GoodwillandIntangibleAssetsDetails" xlink:type="simple" xlink:href="iesc-20250331.xsd#GoodwillandIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.ies-co.com/role/GoodwillandIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_82704b57-d1dc-4387-8901-448b861ddad6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_3c056f9a-8a6b-4309-948d-161ff6b9f5d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_82704b57-d1dc-4387-8901-448b861ddad6" xlink:to="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_3c056f9a-8a6b-4309-948d-161ff6b9f5d2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_46b2c7c3-7896-4d66-a98e-50398eb87feb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_3c056f9a-8a6b-4309-948d-161ff6b9f5d2" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_46b2c7c3-7896-4d66-a98e-50398eb87feb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_46b2c7c3-7896-4d66-a98e-50398eb87feb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_46b2c7c3-7896-4d66-a98e-50398eb87feb" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_46b2c7c3-7896-4d66-a98e-50398eb87feb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_fd022902-27b7-4a57-b454-8eec2ea12b14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_46b2c7c3-7896-4d66-a98e-50398eb87feb" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_fd022902-27b7-4a57-b454-8eec2ea12b14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_iesc_ArrowEngineCompanyMember_253c12e8-d283-4b3a-81fe-a2bcb01e8628" xlink:href="iesc-20250331.xsd#iesc_ArrowEngineCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_fd022902-27b7-4a57-b454-8eec2ea12b14" xlink:to="loc_iesc_ArrowEngineCompanyMember_253c12e8-d283-4b3a-81fe-a2bcb01e8628" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecurringAdjustmentAxis_ce6fb6f5-63ae-49e0-a881-f3d817b7c7c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonrecurringAdjustmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_3c056f9a-8a6b-4309-948d-161ff6b9f5d2" xlink:to="loc_us-gaap_NonrecurringAdjustmentAxis_ce6fb6f5-63ae-49e0-a881-f3d817b7c7c7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecurringAdjustmentDomain_ce6fb6f5-63ae-49e0-a881-f3d817b7c7c7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonrecurringAdjustmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_NonrecurringAdjustmentAxis_ce6fb6f5-63ae-49e0-a881-f3d817b7c7c7" xlink:to="loc_us-gaap_NonrecurringAdjustmentDomain_ce6fb6f5-63ae-49e0-a881-f3d817b7c7c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecurringAdjustmentDomain_94569bd3-4383-4f06-9e00-711b1a0597ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonrecurringAdjustmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_NonrecurringAdjustmentAxis_ce6fb6f5-63ae-49e0-a881-f3d817b7c7c7" xlink:to="loc_us-gaap_NonrecurringAdjustmentDomain_94569bd3-4383-4f06-9e00-711b1a0597ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_dd73c8f2-e6e3-4fef-ae87-8f5dfa3c9412" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionsProFormaRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_82704b57-d1dc-4387-8901-448b861ddad6" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_dd73c8f2-e6e3-4fef-ae87-8f5dfa3c9412" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_31c08804-4446-4185-b883-f0917e99e931" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_82704b57-d1dc-4387-8901-448b861ddad6" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_31c08804-4446-4185-b883-f0917e99e931" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-roles-2025.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationIntegrationRelatedCosts" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationIntegrationRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementAbstract" xlink:to="loc_us-gaap_BusinessCombinationIntegrationRelatedCosts" xlink:type="arc" order="691"/>
  </link:definitionLink>
</link:linkbase>
