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      <submissionType>144</submissionType>
      <filerInfo>
        <filer>
          <filerCredentials>
            <cik>0001185998</cik>
            <ccc>XXXXXXXX</ccc>
          </filerCredentials>
        </filer>
        <liveTestFlag>LIVE</liveTestFlag>
  
  
  
      </filerInfo>
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    <formData>
      <issuerInfo>
        <issuerCik>0000354190</issuerCik>
        <issuerName>Arthur J. Gallagher &amp; Co.</issuerName>
        <secFileNumber>001-09761</secFileNumber>
        <issuerAddress>
          <com:street1>2850 GOLF ROAD</com:street1>
          <com:city>ROLLING MEADOWS</com:city>
          <com:stateOrCountry>IL</com:stateOrCountry>
          <com:zipCode>60008-4050</com:zipCode>
        </issuerAddress>
        <issuerContactPhone>630-773-3800</issuerContactPhone>
        <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>CARY RICHARD C</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
        <relationshipsToIssuer>
          <relationshipToIssuer>Officer</relationshipToIssuer>
        </relationshipsToIssuer>
      </issuerInfo>
      <securitiesInformation>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <brokerOrMarketmakerDetails>
          <name>Fidelity Brokerage Services LLC</name>
          <address>
            <com:street1>900 Salem Street</com:street1>
            <com:city>Smithfield</com:city>
            <com:stateOrCountry>RI</com:stateOrCountry>
            <com:zipCode>02917</com:zipCode>
          </address>
        </brokerOrMarketmakerDetails>
        <noOfUnitsSold>12000</noOfUnitsSold>
        <aggregateMarketValue>4074116.39</aggregateMarketValue>
        <noOfUnitsOutstanding>256100000</noOfUnitsOutstanding>
        <approxSaleDate>05/07/2025</approxSaleDate>
        <securitiesExchangeName>NYSE</securitiesExchangeName>
      </securitiesInformation>
      <securitiesToBeSold>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <acquiredDate>11/05/2024</acquiredDate>
        <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
        <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
        <isGiftTransaction>N</isGiftTransaction>
        <amountOfSecuritiesAcquired>12000</amountOfSecuritiesAcquired>
        <paymentDate>11/05/2024</paymentDate>
        <natureOfPayment>Compensation</natureOfPayment>
      </securitiesToBeSold>
      <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
      <securitiesSoldInPast3Months>
        <sellerDetails>
          <name>Richard C. Cary</name>
          <address>
            <com:street1>2850 Golf Road</com:street1>
            <com:city>Rolling Meadows</com:city>
            <com:stateOrCountry>IL</com:stateOrCountry>
            <com:zipCode>60008</com:zipCode>
          </address>
        </sellerDetails>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <saleDate>02/10/2025</saleDate>
        <amountOfSecuritiesSold>10000</amountOfSecuritiesSold>
        <grossProceeds>3229895.01</grossProceeds>
      </securitiesSoldInPast3Months>
      <noticeSignature>
        <noticeDate>05/07/2025</noticeDate>
        <signature>/s/ Jared Cook, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Richard C. Cary</signature>
      </noticeSignature>
    </formData>
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text: 144
  0001185998
  XXXXXXXX
  LIVE
  0000354190
  Arthur J. Gallagher & Co.
  001-09761
  2850 GOLF ROAD
  ROLLING MEADOWS
  IL
  60008-4050
  630-773-3800
  CARY RICHARD C
  Officer
  Common
  Fidelity Brokerage Services LLC
  900 Salem Street
  Smithfield
  RI
  02917
  12000
  4074116.39
  256100000
  05/07/2025
  NYSE
  Common
  11/05/2024
  Restricted Stock Vesting
  Issuer
  N
  12000
  11/05/2024
  Compensation
  N
  Richard C. Cary
  2850 Golf Road
  Rolling Meadows
  IL
  60008
  Common
  02/10/2025
  10000
  3229895.01
  05/07/2025
  /s/ Jared Cook, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Richard C. Cary