IL-1120-ST-X: Amended Small Business Corporation Replacement Tax Return (2024)
Illinois · Illinois DOR · Used for tax years 2024
Form IL-1120-ST-X is Illinois’s Amended Small Business Corporation Replacement Tax Return. It reports corrected income, deductions, taxes, and pass-through withholding and calculates any refund or additional tax due.
Who files this form
Form IL-1120-ST-X is for a small business corporation amending its Illinois replacement tax return. The form provides boxes for a net loss deduction (NLD), state change, or federal change.
The 2024 version is for tax years ending on or after December 31, 2024. Do not use it to amend a tax year ending before December 31, 2024.
What you'll need
Have your corporation’s legal name, mailing address, federal employer identification number (FEIN), NAICS code, and Illinois corporate file number ready. You will also need the amounts most recently reported or adjusted and the corrected amounts.
Prepare an explanation of the changes. Attach a separate sheet if needed.
Attach the documents that apply to your entries, including:
- Federal changes: Your federal finalization document.
- Income and adjustments: Federal Schedule K and Form 1120S provide information used on the return. Required attachments may include Form IL-4562, Schedule 80/20, Schedule M, Schedule 1299-A, Schedule NB, and Schedules K-1-P or K-1-T.
- Shareholder information and withholding: Schedule B and applicable Schedules K-1-P or K-1-T. Attach Forms W-2G for Illinois income tax withholding reported on Line 63d.
- Unitary business groups: Schedule UB.
- Losses and debt adjustments: Schedule NLD for an Illinois net loss deduction, federal Form 982 for a discharge of indebtedness adjustment, and a detailed statement if you have merged losses.
- Investment credits: Schedule 4255 for recaptured credits and Form IL-477 for investment credits.
- Other federal disclosures: Federal Form 8886 and federal Schedule M-3, Part II, Line 10, if completed and not previously attached.
- Annualized PTE tax income: Form IL-2220 if you are paying PTE tax and annualized your income on that form.
- Payment: Form IL-1120-ST-X-V with your payment.
How to file
- Enter the beginning and ending dates of the tax year you are amending, identify the corporation, and check the applicable boxes in Step 1.
- Explain the changes. Enter amounts as most recently reported or adjusted in Column A and corrected amounts in Column B where provided.
- Complete the applicable income, tax, payment, and refund calculations. Attach the required schedules and supporting documents.
- Have an authorized officer sign and date the return and provide their title and phone number.
- If paying, enter the payment amount at the top of Page 1 and attach your payment and Form IL-1120-ST-X-V where indicated.
Mail the return to:
Illinois Department of Revenue
P.O. Box 19016
Springfield, IL 62794-9016
Common mistakes
- Using the wrong version: Do not use this form for tax years ending before December 31, 2024.
- Completing Step 6 incorrectly: If Line 35 income is derived only inside Illinois and you are not a unitary filer, check the Illinois-only box and leave Lines 36 through 46 blank. If any portion is derived outside Illinois, or you are a unitary filer, check the other box and complete all of Step 6. Do not leave Lines 40 through 42 blank.
- Entering negative sales: Lines 40 and 41 cannot be negative. Round the apportionment factor on Line 42 to six decimal places.
- Claiming a loss deduction when Line 49 is zero or negative: Enter zero on Line 50 in that case.
- Completing Schedule B out of order: Read its instructions and complete the required K-1 schedules first. Complete Schedule B, Section B, before Section A. The form warns that not following these instructions may delay processing or lead to requests for more information.
- Leaving out required information: The form warns that failure to provide required information could result in a penalty.
Questions people ask
What if I am filing only to report an increased net loss?
Check Step 1, Box C, if you are filing only to report an increased net loss on Line 49, Column B.
What must I include for a federal change?
Check the federal change box and indicate whether the change is partially agreed or finalized. Enter the finalization date and attach your federal finalization document.
Can I carry an overpayment forward instead of receiving it all as a refund?
Line 70 lets you enter the portion of the Line 69 overpayment to be credited forward. Line 71 shows the remaining refund. If the carryforward is going to a different FEIN, check the box and attach a detailed statement.
Will I receive a bill for additional penalty and interest?
Yes. The form states that you will be sent a bill for any additional penalty and interest.
What if Schedule B does not have enough space for all shareholders?
Attach additional copies of Schedule B, Section B, as needed. Attach all Section B pages behind Section A.