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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-02-20</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001450678</rptOwnerCik>
            <rptOwnerName>RAMLO RANDY A.</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>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President/CEO</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-02-20</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>8371</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>29.12</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>41165</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>29.12</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2015-02-20</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>49067</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2025-02-20</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>49067.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>49067</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This transaction represents a grant of restricted stock shares to the Reporting Person under the Issuer's Stock Plan.</footnote>
        <footnote id="F2">The price per share is the closing price of the Issuer's common stock on the date of the reported transaction.</footnote>
        <footnote id="F3">The total number of securities beneficially held directly by the Reporting Person (excluding frationals) includes: 7,322 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/18/2016; 5,304 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/15/2018; 9,151 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/21/2019; 8,371 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/20/2020; 9,586 shares held of record by the Reporting Person; 531 shares held in a brokerage account by the Reporting Person; and 900 shares held jointly by the Reporting Person and his wife.</footnote>
        <footnote id="F4">Options become vested and exercisable in equal installments on 02/20/2016, 02/20/2017, 02/20/2018, 02/20/2019 and 02/20/2020, respectively.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Randy A. Ramlo by Barrie W. Ernst, Attorney-in-Fact</signatureName>
        <signatureDate>2015-02-23</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2015-02-20
0
0000101199
UNITED FIRE GROUP INC
UFCS
0001450678
RAMLO RANDY A.
118 SECOND AVENUE SE
P.O. BOX 73909
CEDAR RAPIDS
IA
52407-3909
1
1
0
0
President/CEO
Common Stock
2015-02-20
4
A
0
8371
29.12
A
41165
D
Stock Option (right to buy)
29.12
2015-02-20
4
A
0
49067
0
A
2025-02-20
Common
49067.0
49067
D
This transaction represents a grant of restricted stock shares to the Reporting Person under the Issuer's Stock Plan.
The price per share is the closing price of the Issuer's common stock on the date of the reported transaction.
The total number of securities beneficially held directly by the Reporting Person (excluding frationals) includes: 7,322 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/18/2016; 5,304 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/15/2018; 9,151 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/21/2019; 8,371 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/20/2020; 9,586 shares held of record by the Reporting Person; 531 shares held in a brokerage account by the Reporting Person; and 900 shares held jointly by the Reporting Person and his wife.
Options become vested and exercisable in equal installments on 02/20/2016, 02/20/2017, 02/20/2018, 02/20/2019 and 02/20/2020, respectively.
/s/ Randy A. Ramlo by Barrie W. Ernst, Attorney-in-Fact
2015-02-23