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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-09-18</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>2015-09-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>22</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>33.9265</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>11342</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 total number of securities beneficially held directly by the Reporting Person (excluding fractionals) following the reported transaction includes: 3,354 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>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Neal R. Scharmer by Michael T. Wilkins, Attorney-in-Fact</signatureName>
        <signatureDate>2015-09-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2015-09-18
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
2015-09-18
4
J
0
22
33.9265
A
11342
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 total number of securities beneficially held directly by the Reporting Person (excluding fractionals) following the reported transaction includes: 3,354 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.
/s/ Neal R. Scharmer by Michael T. Wilkins, Attorney-in-Fact
2015-09-21