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What federal forms must I attach to my business, trust, or estate return?

When filing your return there are certain types of income items and subtraction modifications that require the attachment of Illinois or federal forms and schedules. Instructions for these attachments appear throughout the current year return instructions. Include only forms and schedules required to support your return. Do not attach correspondence to your return.

Corporations - All taxpayers, including unitary business groups, must attach a copy of all pages of federal Form 1120, and Schedules L, M-1, M-2, and M-3, if applicable, to your Illinois return. However, there are a few exceptions:

  • If you are a corporation, but do not file federal Form 1120, you must attach a copy of the form that you file federally.
  • If you are a corporation whose taxable income is included in a consolidated federal tax return, you must provide a pro forma copy of federal Form 1120, federal Form 1120-L, or federal Form 1120-PC, and all applicable schedules as if you had filed a separate federal return.

See Form IL-1120 instructions for more information.

S corporations - All taxpayers, including unitary business groups, must attach a copy of your federal Form 1120S, U.S. Income Tax Return for an S Corporation, Pages 1 through 5, to your Illinois return if you are required to file federally.

See Form IL-1120-ST instructions for more information.

Partnerships - All taxpayers, including unitary business groups, must attach a copy of your federal Form 1065, U.S. Return of Partnership Income, Pages 1 through 5, to your Illinois return if you are required to file federally.

See Form IL-1065 instructions for more information.

Trusts and Estates - All taxpayers must attach a copy of your federal Form 1041, U.S. Income Tax Return for Estates and Trusts, Pages 1 and 2, to your Illinois return if you are required to file federally.

See Form IL-1041 instructions for more information.

Exempt Organizations - All taxpayers must attach a copy of your federal Form 990-T, Exempt Organization Business Income Tax Return, Page 1, to your Illinois return if you are required to file federally.

See Form IL-990-T instructions for more information.

 

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