IL-1120-ST: Small Business Corporation Replacement Tax Return (2025)
Illinois · Illinois DOR · Used for tax years 2025
Form IL-1120-ST is the Illinois Small Business Corporation Replacement Tax Return. It reports income or loss, Illinois adjustments, replacement tax, applicable surcharges, pass-through withholding, and pass-through entity tax, and calculates a refund or balance due.
When it's due
For the 2025 Form IL-1120-ST, the return is due on or before the 15th day of the 3rd month following the close of the tax year.
This version is for tax years ending on or after December 31, 2025, and before December 31, 2026. If your return is not for calendar year 2025, enter your fiscal tax year's beginning and ending dates.
What you'll need
Have your business identification and tax information ready:
- Complete legal business name, mailing address, FEIN, NAICS code, and Illinois corporate file number.
- City, state, and ZIP code where your accounting records are kept.
- Federal Schedule K and federal Form 1120-S information used to figure income and deductions.
- Records of payments, previous overpayment credits, and withholding reported to you.
Attach supporting forms and schedules when they apply:
- Income adjustments: Form IL-4562, Schedule 80/20, Illinois Schedule M for businesses, Schedule 1299-A, and Schedules K-1-P or K-1-T.
- Shareholder information and withholding: Schedule B. Its directions require completing the applicable Schedules K-1-P and K-1-P(3) or K-1-P(4) first.
- Unitary business reporting or nonbusiness income: Schedule UB or Schedule NB, as applicable.
- Loss deductions and debt adjustments: Schedule NLD and federal Form 982, as applicable. Attach a detailed statement for merged losses.
- Investment credits: Form IL-477 or Schedule 4255, as applicable.
- Withholding claimed: Schedules K-1-P or K-1-T and Forms W-2G, as applicable.
If you completed federal Form 8886 or federal Schedule M-3, Part II, Line 10, check the applicable box and attach the federal form. If you are paying pass-through entity tax and annualized your income on Form IL-2220, check Step 1, Box M, and attach Form IL-2220.
How to file
Complete the return and applicable attachments. An authorized officer must sign Step 11 and provide the date, title, and phone number.
If enclosing a payment, attach your payment and Form IL-1120-ST-V in the designated space. Enter the payment amount at the top of Page 1. Mail the return to:
Illinois Department of Revenue
P.O. Box 19053
Springfield, IL 62794-9053
If not enclosing a payment, mail the return to:
Illinois Department of Revenue
P.O. Box 19032
Springfield, IL 62794-9032
Common mistakes
- Completing Step 6 when it must be blank. If your income is derived only inside Illinois and you are not a unitary filer, check Step 5, Box A, carry Line 35 to Line 47, and leave Lines 36 through 46 blank.
- Skipping Step 6 when it is required. Unitary filers and filers with any income derived outside Illinois must check Step 5, Box B, and complete all lines of Step 6. Do not leave Lines 40 through 42 blank.
- Entering negative sales amounts. Lines 40 and 41 cannot be negative. Round the apportionment factor on Line 42 to six decimal places.
- Completing Schedule B in the wrong order. Complete the required shareholder schedules and Section B before Section A. The form warns that not following these directions may delay processing or lead to requests for more information.
- Forgetting the payment amount on Page 1. The form specifically reminds you to enter it in the space provided.
- Leaving out required information. The form warns that failure to provide required information could result in a penalty.
Questions people ask
How is replacement tax calculated on this form?
Line 52 instructs you to multiply net income on Line 51 by 1.5% (.015). Later lines account for investment credit recapture and investment credits.
How do I indicate that I elected to file and pay pass-through entity tax?
Check Step 1, Box L.
Can I have my refund deposited directly into my bank account?
The form provides a direct deposit option on Line 70. Enter your routing number and account number, and select checking or savings.
What if Schedule B does not have enough room for all shareholders?
Attach additional copies of Section B as needed. Attach all Section B pages behind the Schedule B Section A page.
What information is needed for a final return?
Check the final return box and enter the termination date. If the return is final because you sold the business, also enter the sale date and the new owner's FEIN.