When must I file an amended return?
- you discover that you made an error on your Illinois return after it was filed, or
- your federal return has been adjusted either by the Internal Revenue Service (IRS) or on a 1040X, Amended U.S. Individual Income Tax Return, you filed; the change affects your Illinois income, additions, subtractions, exemptions, or credits; and the change is final.
Do not file another Form IL-1040 to make changes to a previously filed Form IL-1040. You must file Form IL-1040-X, Amended Individual Income Tax Return, if
NOTE: If the federal change results in a refund, do not file Form IL-1040-X until you receive notification that your change has been accepted by the IRS. You must submit this notification (federal finalization) when you submit your IL-1040-X.
For more information, see Form IL-1040-X instructions.
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