Mailing addresses for Forms 941 ; Department of the Treasury Internal Revenue Service Kansas City, MO 64999-0005. Internal Revenue Service PO Box 806532Mailing addresses are provided for taxpayers and tax practitioners filing Form 941-X. Yes file your 1st quarter employment tax return on form 941 and pay missing payment as soon as possible. This guide provides the basics of the 941 form, instructions to help you fill it out, and where you can get help meeting all your payroll tax obligations. Overpayment as a nonemployee, file Form 941 for each delinquent quarter.