If you need to correct or change your return after it has been filed, you must file Form IL-1120-ST-X, Amended Small Business Corporation Replacement Tax Return, for the appropriate year. Any correction made may cause a recalculation of penalties and interest. For more information refer to the Form IL-1120-ST-X Instructions for the year you wish to amend. Click the following links for the current year amended form and instructions:
If you have additional inquiries, you may submit them to the Questions, Comments, or Request form.