-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 C8W8tqucldU4s1lm2T0eWs3ZBtiyEJl6lzIFdBuATDw/GKKmvdZKQ6OYgNKNwvR/
 lWQzOwKJuIuNzpk55kjEHg==

<SEC-DOCUMENT>0001179110-04-000585.txt : 20040106
<SEC-HEADER>0001179110-04-000585.hdr.sgml : 20040106
<ACCEPTANCE-DATETIME>20040106182844
ACCESSION NUMBER:		0001179110-04-000585
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20040102
FILED AS OF DATE:		20040106

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			BUNGERT MICHAEL G
		CENTRAL INDEX KEY:			0001269436

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-07933
		FILM NUMBER:		04511356

	BUSINESS ADDRESS:	
		STREET 1:		AON CORP.
		STREET 2:		200 EAST RANDOLPH STREET
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60601

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			AON CORP
		CENTRAL INDEX KEY:			0000315293
		STANDARD INDUSTRIAL CLASSIFICATION:	ACCIDENT & HEALTH INSURANCE [6321]
		IRS NUMBER:				363051915
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		200 EAST RANDOLPH STREET
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60601
		BUSINESS PHONE:		3123811000

	MAIL ADDRESS:	
		STREET 1:		200 EAST RANDOLPH STREET
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60601

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	COMBINED INTERNATIONAL CORP
		DATE OF NAME CHANGE:	19870504
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>
<periodOfReport>2004-01-02</periodOfReport>
<notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000315293</issuerCik>
        <issuerName>AON CORP</issuerName>
        <issuerTradingSymbol>AOC</issuerTradingSymbol>
</issuer>
<reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001269436</rptOwnerCik>
            <rptOwnerName>BUNGERT MICHAEL G</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>AON CORPORATION - CORPORATE LAW DEPT</rptOwnerStreet1>
            <rptOwnerStreet2>200 EAST RANDOLPH STREET, 8TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>CHICAGO</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60601</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>0</isDirector>
<isOfficer>1</isOfficer>
<isTenPercentOwner>0</isTenPercentOwner>
<isOther>0</isOther>
<officerTitle>Aon Re Inc. - President/CEO</officerTitle>
<otherText></otherText>
</reportingOwnerRelationship>
</reportingOwner>
<nonDerivativeTable><nonDerivativeHolding><securityTitle><value>Common Stock</value>
</securityTitle>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>105716</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</nonDerivativeHolding>
<nonDerivativeHolding><securityTitle><value>Common Stock</value>
</securityTitle>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>31466</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>I</value>
</directOrIndirectOwnership>
<natureOfOwnership><value>Through Aon Savings Plan and ESOP</value>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeHolding>
</nonDerivativeTable>
<derivativeTable><derivativeTransaction><securityTitle><value>Stock Award (Right to Receive)</value>
</securityTitle>
<conversionOrExercisePrice><value>0</value>
</conversionOrExercisePrice>
<transactionDate><value>2004-01-02</value>
</transactionDate>
<transactionCoding><transactionFormType>4</transactionFormType>
<transactionCode>A</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved>
</transactionCoding>
<transactionAmounts><transactionShares><value>22500</value>
</transactionShares>
<transactionPricePerShare><value>0</value>
</transactionPricePerShare>
<transactionAcquiredDisposedCode><value>A</value>
</transactionAcquiredDisposedCode>
</transactionAmounts>
<exerciseDate><value>2007-01-02</value>
<footnoteId id="F1"></footnoteId>
</exerciseDate>
<expirationDate><value>2014-01-02</value>
</expirationDate>
<underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value>
</underlyingSecurityTitle>
<underlyingSecurityShares><value>22500</value>
</underlyingSecurityShares>
</underlyingSecurity>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>22500</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</derivativeTransaction>
</derivativeTable>
<footnotes><footnote id="F1">Awards will vest in accordance with the Aon Stock Incentive Plan as follows; 20% of the awards will vest on each of the third and tenth anniversaries of the date of grant, and 10% of the awards will vest on each of the fourth through ninth anniversaries of the date of grant.</footnote>
</footnotes>
<ownerSignature><signatureName>/s/ Jennifer L. Kraft - by Jennifer L. Kraft pursuant to a power of attorney from Michael G. Bungert</signatureName>
<signatureDate>2004-01-06</signatureDate>
</ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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