You may amend your Illinois income tax return due to either changes in your federal income tax return or because of entirely state changes. The form you file depends on the form on which you used for your original return. Use the amendment form for the same year that you are amending. All forms are available through the Illinois Department of Revenue website.
Assess time requirements. If you are filing an amended return because of only state changes in income or deductions, you must do so within three years of the taxes being due or the original return being filed, or one year from the taxes being paid, whichever is latest. If you are reporting changes to your federal income tax, you have two years plus 120 days from the finalization of those changes to file an amended Illinois return.
File a 1040-X if you filed an IL-1040. If you filed your state tax return on a form IL-1040, your amended return should be filed on form IL-1040-X. Attach a copy of your amended U.S. tax return and a copy of your refund check or other IRS notification accepting your amended federal return.
File an 843 if you filed an IL-1041, IL-1023-C or IL-990-T. If you had a change in income and filed a form IL-1041, IL-1023-C or IL-990-T, you can report this change on form IL-843. You must attach a revised copy of the original Illinois tax form, including any schedules.
Your amended return may be denied. If this occurs, you will be notified in writing, from which time you will have 60 days to request a hearing. If you do not receive acceptance or denial of your amended return within six months, you may request a hearing in writing.
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