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    <filerInfo>
      <filer>
        <filerCredentials>
          <cik>0001386997</cik>
          <ccc>XXXXXXXX</ccc>
        </filerCredentials>
      </filer>
      <liveTestFlag>LIVE</liveTestFlag>



    </filerInfo>
  </headerData>
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    <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>Pietrucha Susan E</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>57419</noOfUnitsSold>
      <aggregateMarketValue>12127248.58</aggregateMarketValue>
      <noOfUnitsOutstanding>212094000</noOfUnitsOutstanding>
      <approxSaleDate>05/03/2023</approxSaleDate>
      <securitiesExchangeName>NYSE</securitiesExchangeName>
    </securitiesInformation>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>03/11/2020</acquiredDate>
      <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>1392</amountOfSecuritiesAcquired>
      <paymentDate>03/11/2020</paymentDate>
      <natureOfPayment>Compensation</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>03/31/2020</acquiredDate>
      <natureOfAcquisitionTransaction>ESPP Purchase</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>262</amountOfSecuritiesAcquired>
      <paymentDate>03/31/2020</paymentDate>
      <natureOfPayment>Cash</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>03/15/2021</acquiredDate>
      <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>5678</amountOfSecuritiesAcquired>
      <paymentDate>03/15/2021</paymentDate>
      <natureOfPayment>Compensation</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>03/17/2021</acquiredDate>
      <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>2562</amountOfSecuritiesAcquired>
      <paymentDate>03/17/2021</paymentDate>
      <natureOfPayment>Compensation</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>03/31/2021</acquiredDate>
      <natureOfAcquisitionTransaction>ESPP Purchase</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>58</amountOfSecuritiesAcquired>
      <paymentDate>03/31/2021</paymentDate>
      <natureOfPayment>Cash</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>06/30/2021</acquiredDate>
      <natureOfAcquisitionTransaction>ESPP Purchase</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>142</amountOfSecuritiesAcquired>
      <paymentDate>06/30/2021</paymentDate>
      <natureOfPayment>Cash</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>03/14/2022</acquiredDate>
      <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>4877</amountOfSecuritiesAcquired>
      <paymentDate>03/14/2022</paymentDate>
      <natureOfPayment>Compensation</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>03/16/2022</acquiredDate>
      <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>2143</amountOfSecuritiesAcquired>
      <paymentDate>03/16/2022</paymentDate>
      <natureOfPayment>Compensation</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>03/31/2022</acquiredDate>
      <natureOfAcquisitionTransaction>ESPP Purchase</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>42</amountOfSecuritiesAcquired>
      <paymentDate>03/31/2022</paymentDate>
      <natureOfPayment>Cash</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>06/30/2022</acquiredDate>
      <natureOfAcquisitionTransaction>ESPP Purchase</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>102</amountOfSecuritiesAcquired>
      <paymentDate>06/30/2022</paymentDate>
      <natureOfPayment>Cash</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>03/12/2023</acquiredDate>
      <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>5467</amountOfSecuritiesAcquired>
      <paymentDate>03/12/2023</paymentDate>
      <natureOfPayment>Compensation</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>03/15/2023</acquiredDate>
      <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>1920</amountOfSecuritiesAcquired>
      <paymentDate>03/15/2023</paymentDate>
      <natureOfPayment>Compensation</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>03/31/2023</acquiredDate>
      <natureOfAcquisitionTransaction>ESPP Purchase</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>74</amountOfSecuritiesAcquired>
      <paymentDate>03/31/2023</paymentDate>
      <natureOfPayment>Cash</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>05/03/2023</acquiredDate>
      <natureOfAcquisitionTransaction>Option Granted - 03/16/2017</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>18400</amountOfSecuritiesAcquired>
      <paymentDate>05/03/2023</paymentDate>
      <natureOfPayment>Cash</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>05/03/2023</acquiredDate>
      <natureOfAcquisitionTransaction>Option Granted - 03/15/2018</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>14300</amountOfSecuritiesAcquired>
      <paymentDate>05/03/2023</paymentDate>
      <natureOfPayment>Cash</natureOfPayment>
    </securitiesToBeSold>
    <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
    <noticeSignature>
      <noticeDate>05/03/2023</noticeDate>
      <signature>/s/ Jennifer Ruchti, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Susan Pietrucha</signature>
    </noticeSignature>
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[{"type": "144", "sequence": "1", "filename": "primary_doc.xml", "secsgml_size_bytes": 10257}]
144
0001386997
XXXXXXXX
LIVE
0000354190
Arthur J. Gallagher & Co.
001-09761
2850 GOLF ROAD
ROLLING MEADOWS
IL
60008-4050
630-773-3800
Pietrucha Susan E
Officer
Common
Fidelity Brokerage Services LLC
900 Salem Street
Smithfield
RI
02917
57419
12127248.58
212094000
05/03/2023
NYSE
Common
03/11/2020
Restricted Stock Vesting
Issuer
N
1392
03/11/2020
Compensation
Common
03/31/2020
ESPP Purchase
Issuer
N
262
03/31/2020
Cash
Common
03/15/2021
Restricted Stock Vesting
Issuer
N
5678
03/15/2021
Compensation
Common
03/17/2021
Restricted Stock Vesting
Issuer
N
2562
03/17/2021
Compensation
Common
03/31/2021
ESPP Purchase
Issuer
N
58
03/31/2021
Cash
Common
06/30/2021
ESPP Purchase
Issuer
N
142
06/30/2021
Cash
Common
03/14/2022
Restricted Stock Vesting
Issuer
N
4877
03/14/2022
Compensation
Common
03/16/2022
Restricted Stock Vesting
Issuer
N
2143
03/16/2022
Compensation
Common
03/31/2022
ESPP Purchase
Issuer
N
42
03/31/2022
Cash
Common
06/30/2022
ESPP Purchase
Issuer
N
102
06/30/2022
Cash
Common
03/12/2023
Restricted Stock Vesting
Issuer
N
5467
03/12/2023
Compensation
Common
03/15/2023
Restricted Stock Vesting
Issuer
N
1920
03/15/2023
Compensation
Common
03/31/2023
ESPP Purchase
Issuer
N
74
03/31/2023
Cash
Common
05/03/2023
Option Granted - 03/16/2017
Issuer
N
18400
05/03/2023
Cash
Common
05/03/2023
Option Granted - 03/15/2018
Issuer
N
14300
05/03/2023
Cash
Y
05/03/2023
/s/ Jennifer Ruchti, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Susan Pietrucha