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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-01-23</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000101199</issuerCik>
        <issuerName>UNITED FIRE GROUP INC</issuerName>
        <issuerTradingSymbol>UFCS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001550220</rptOwnerCik>
            <rptOwnerName>Carlton Scott L</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>118 SECOND AVENUE SE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CEDAR RAPIDS</rptOwnerCity>
            <rptOwnerState>IA</rptOwnerState>
            <rptOwnerZipCode>52041</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-01-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>G</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value>E</value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1720</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>36260</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>by Reporting Person's children</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">The number of shares held indirectly by the Reporting Person includes: 13,190 shares held for the benefit of the Reporting Person's son, 11,190 shares held for the benefit of the ReportingPerson's son, 7,390 shares held for the benefit of the Reporting Person's daughter and 4,490 shares held for the benefit of the Reporting Person's daughter.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Scott L. Carlton by Barrie W. Ernst, Attorney-in-Fact</signatureName>
        <signatureDate>2015-01-26</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2015-01-23
0
0000101199
UNITED FIRE GROUP INC
UFCS
0001550220
Carlton Scott L
118 SECOND AVENUE SE
CEDAR RAPIDS
IA
52041
1
0
0
0
Common Stock
2015-01-23
5
G
0
E
1720
0
A
36260
I
by Reporting Person's children
The number of shares held indirectly by the Reporting Person includes: 13,190 shares held for the benefit of the Reporting Person's son, 11,190 shares held for the benefit of the ReportingPerson's son, 7,390 shares held for the benefit of the Reporting Person's daughter and 4,490 shares held for the benefit of the Reporting Person's daughter.
/s/ Scott L. Carlton by Barrie W. Ernst, Attorney-in-Fact
2015-01-26