If you discover that you made an error on your return after it was filed or if your federal return was adjusted by the Internal Revenue Service (IRS), you should file an amended Illinois return using
Form IL-1040-X, Amended Individual Income Tax Return. If you are filing Form IL-1040-X due to a federal change, do not file it until you receive notification from the IRS showing it was accepted. For more information, refer to the
Form IL-1040-X Instructions.
