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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 Rya6UIwADM8QwoTyz/CNDyoLbVIPJxiLbstfRrExvnObTYzZ/oGvhRbh7trvORAi
 MWM3JZmbVvw3zKlTpkXFaQ==

<SEC-DOCUMENT>0001179110-05-011432.txt : 20050611
<SEC-HEADER>0001179110-05-011432.hdr.sgml : 20050611
<ACCEPTANCE-DATETIME>20050602112826
ACCESSION NUMBER:		0001179110-05-011432
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20050525
FILED AS OF DATE:		20050602
DATE AS OF CHANGE:		20050602

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MAINSOURCE FINANCIAL GROUP
		CENTRAL INDEX KEY:			0000720002
		STANDARD INDUSTRIAL CLASSIFICATION:	STATE COMMERCIAL BANKS [6022]
		IRS NUMBER:				351562245
		STATE OF INCORPORATION:			IN
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		201 N BROADWAY
		STREET 2:		PO BOX 87
		CITY:			GREENSBURG
		STATE:			IN
		ZIP:			47240
		BUSINESS PHONE:		8126630157

	MAIL ADDRESS:	
		STREET 1:		201 NORTH BROADWAY
		STREET 2:		P O BOX 87
		CITY:			GREENSBURG
		STATE:			IN
		ZIP:			47240

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	INDIANA UNITED BANCORP
		DATE OF NAME CHANGE:	19920703

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Crall Brian J
		CENTRAL INDEX KEY:			0001328642

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-12422
		FILM NUMBER:		05872632

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		502-227-0033

	MAIL ADDRESS:	
		STREET 1:		101 PORTSMOUTH LANE
		CITY:			FRANKFORT
		STATE:			KY
		ZIP:			40601
</SEC-HEADER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 3 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2005-05-25</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000720002</issuerCik>
        <issuerName>MAINSOURCE FINANCIAL GROUP</issuerName>
        <issuerTradingSymbol>MSFG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001328642</rptOwnerCik>
            <rptOwnerName>Crall Brian J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>101 PORTSMOUTH LANE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>FRANKFORT</rptOwnerCity>
            <rptOwnerState>KY</rptOwnerState>
            <rptOwnerZipCode>40601</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Initial filing - Mr. Crall was elected to the board of directors of MainSource Financial Group at the shareholders meeting held May 25, 2005.  Mr. Crall does not currently own any shares of MSFG.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Brian J. Crall</signatureName>
        <signatureDate>2005-06-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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