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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-06-30</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001601293</rptOwnerCik>
            <rptOwnerName>Voss Susan E</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>118 SECOND AVENUE SE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CEDAR RAPIDS</rptOwnerCity>
            <rptOwnerState>IA</rptOwnerState>
            <rptOwnerZipCode>52401-1212</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>2015-09-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>18</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>34.2251</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2869</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-06-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>19</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>31.2219</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2888</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Shares acquired through participation in the Issuer's Dividend Reinvestment Plan.</footnote>
        <footnote id="F2">Represents the approximate number of shares (excluding fractionals) acquired by the Reporting Person through the Issuer's Dividend Reinvestment Plan.</footnote>
        <footnote id="F3">The number of shares beneficially held directly by the Reporting Person following the reported transaction includes: 593 shared held directly by Ms. Voss and 2,295 shares of restricted stock issued to Ms. Voss under the Issuer's Non-Qualified Non-Employee Stock Option and Restricted Stock Plan which vest, subject to certain conditions, by May 21, 2018.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Susan E. Voss by Michael T. Wilkins, Attorney-in-Fact</signatureName>
        <signatureDate>2015-09-23</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2015-06-30
0
0000101199
UNITED FIRE GROUP INC
UFCS
0001601293
Voss Susan E
118 SECOND AVENUE SE
CEDAR RAPIDS
IA
52401-1212
1
0
0
0
Common Stock
2015-09-18
4
J
0
18
34.2251
A
2869
D
Common Stock
2015-06-30
4
J
0
19
31.2219
A
2888
D
Shares acquired through participation in the Issuer's Dividend Reinvestment Plan.
Represents the approximate number of shares (excluding fractionals) acquired by the Reporting Person through the Issuer's Dividend Reinvestment Plan.
The number of shares beneficially held directly by the Reporting Person following the reported transaction includes: 593 shared held directly by Ms. Voss and 2,295 shares of restricted stock issued to Ms. Voss under the Issuer's Non-Qualified Non-Employee Stock Option and Restricted Stock Plan which vest, subject to certain conditions, by May 21, 2018.
/s/ Susan E. Voss by Michael T. Wilkins, Attorney-in-Fact
2015-09-23