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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-04-02</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001451184</rptOwnerCik>
            <rptOwnerName>SCHARMER NEAL R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>118 SECOND AVENUE SE</rptOwnerStreet1>
            <rptOwnerStreet2>P.O. BOX 73909</rptOwnerStreet2>
            <rptOwnerCity>CEDAR RAPIDS</rptOwnerCity>
            <rptOwnerState>IA</rptOwnerState>
            <rptOwnerZipCode>52407-3909</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>VP/General Counsel/Corp Sec</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-04-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3029</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>32</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>14325</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-04-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3029</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>20.54</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>11296</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>20.54</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2015-04-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3029</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2021-02-18</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>3029.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2020</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The total number of securities beneficially held directly by the Reporting Person (excluding fractionals) following the reported transaction includes: 3,287 shares held by Mr. Scharmer; 1,974 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/18/2016; 1,446 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/15/2018; and 2,484 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/21/2019; and 2,083 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/20/2020.</footnote>
        <footnote id="F2">3,029 options currently exercisable. Remaining options become vested and exercisable in equal installments on 02/18/2015 and 02/18/2016, respectively.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Neal R. Scharmer by Michael T. Wilkins, Attorney-in-Fact</signatureName>
        <signatureDate>2015-04-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2015-04-02
0
0000101199
UNITED FIRE GROUP INC
UFCS
0001451184
SCHARMER NEAL R
118 SECOND AVENUE SE
P.O. BOX 73909
CEDAR RAPIDS
IA
52407-3909
0
1
0
0
VP/General Counsel/Corp Sec
Common Stock
2015-04-02
4
J
0
3029
32
A
14325
D
Common Stock
2015-04-02
4
J
0
3029
20.54
D
11296
D
Stock Option (right to buy)
20.54
2015-04-02
4
M
0
3029
0
D
2021-02-18
Common Stock
3029.0
2020
D
The total number of securities beneficially held directly by the Reporting Person (excluding fractionals) following the reported transaction includes: 3,287 shares held by Mr. Scharmer; 1,974 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/18/2016; 1,446 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/15/2018; and 2,484 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/21/2019; and 2,083 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/20/2020.
3,029 options currently exercisable. Remaining options become vested and exercisable in equal installments on 02/18/2015 and 02/18/2016, respectively.
/s/ Neal R. Scharmer by Michael T. Wilkins, Attorney-in-Fact
2015-04-07