<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2011-05-06</periodOfReport>

    <dateOfOriginalSubmission>2011-05-10</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000800457</issuerCik>
        <issuerName>DONEGAL GROUP INC</issuerName>
        <issuerTradingSymbol>DGICA</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000935596</rptOwnerCik>
            <rptOwnerName>DONEGAL MUTUAL INSURANCE CO</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1195 RIVER ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>MARIETTA</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>17547</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2011-05-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>599231</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>13.15</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7755953</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Class B Common Stock</value>
                <footnoteId id="F2"/>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4198839</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Donegal Mutual Insurance Company (&quot;Donegal Mutual&quot;) reported on May 10, 2011 that it had transferred 600,000 shares of Class A common stock of Donegal Group Inc. (&quot;DGI&quot;) to Donegal Financial Services Corporation (&quot;DFSC&quot;) and that DFSC would transfer those shares as merger consideration to the stockholders of Union National Financial Corporation (&quot;UNFC&quot;) in connection with the merger of UNFC with and into DFSC that was effective on May 6, 2011.  DFSC's exchange agent subsequently notified DFSC that, pursuant to the terms of the merger agreement, 599,231 shares of DGI Class A common stock were required for transfer to stockholders of UNFC.  As a result, DFSC returned 769 shares of DGI Class A common stock to Donegal Mutual Insurance Company on June 6, 2011.  This amended Form 4 reflects this immaterial adjustment to the number of shares contributed to DFSC for transfer as merger consideration to UNFC stockholders.</footnote>
        <footnote id="F2">Donegal Mutual's holdings of DGI Class B common stock reflect a subsequent purchase of 500 shares on May 18, 2011 as reported on a Form 4 on May 19, 2011.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Jeffrey D. Miller, Sr. VP &amp; Chief Financial Officer</signatureName>
        <signatureDate>2011-06-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
