This form is for tax years ending on or after December 31, 2025, and before December 31, 2026. For all other situations, see instructions to determine the correct form to use.
Fiscal year: if this return is not for calendar year 2025, enter your fiscal tax year.
First or final return: if this is the first or final return, check the applicable box(es).
Pass-through Entity Tax: check this box if you elected to file and pay Pass-through Entity Tax.
FEIN: enter your federal employer identification number (FEIN).
Payment: attach your payment and Form IL-1120-ST-V.
| Question | Answer |
|---|---|
| Form Name | Form IL-1120-ST |
| Form Length | 5 pages |
| Fillable? | Yes |
| Fillable fields | 370 |
| Avg. time to fill out | 60+ min |
| Edition | R-12/25 |
| Issuing agency | Illinois Department of Revenue |
| Matches the agency's file | Yes, checked October 4, 2026 |
| Other names | IL-1120-ST, IL 1120 ST, Form IL-1120-ST, Illinois 1120-ST, Small Business Corporation Replacement Tax Return |
| Official source | Form IL-1120-ST (Rev R-12/25), Illinois Department of Revenue |
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