IL-1120-X: Amended Corporation Income and Replacement Tax Return (2024)
Illinois · Illinois DOR · Used for tax years 2024
Form IL-1120-X is Illinois’s Amended Corporation Income and Replacement Tax Return. It compares previously reported or adjusted amounts with corrected income, deductions, credits, and taxes to determine a refund or additional tax due.
Who files this form
Form IL-1120-X is for corporations amending an Illinois Corporation Income and Replacement Tax Return.
The 2024 version is for tax years ending on or after December 31, 2024. Do not use this version to amend a tax year ending before December 31, 2024.
The form includes boxes for state changes, federal changes, and net loss deduction changes.
What you'll need
Gather the information and attachments that apply to your changes:
- Corporation details: Legal business name, mailing address, FEIN, NAICS code, Illinois corporate file number, and the beginning and ending dates of the tax year being amended.
- Previously reported and corrected amounts: The form asks for amounts as most recently reported or adjusted in Column A and corrected amounts in Column B.
- Federal documents: Page 4 lists federal Form 1120-X, plus federal Form 1139 or a federal RAR if applicable. For a federal change, attach your federal finalization. If Line 1 changes, examples of finalization documents include a federal refund check copy, IRS audit report, or federal transcript verifying federal taxable income.
- Supporting schedules: Attach the schedules required for the lines you complete. Examples include Form IL-4562 for special depreciation, Schedule 80/20 for related-party expenses, Schedule M for other additions or subtractions, and Schedule NLD or UB/NLD for an Illinois net loss deduction.
- Payment and withholding support: Attach applicable Schedules K-1-P or K-1-T for pass-through withholding or pass-through entity tax credits, and copies of all Forms W-2G for Illinois income tax withholding.
- Other required support: Attach any and all out-of-state returns if Lines 28 through 30 change. Attach federal Form 982 for a discharge of indebtedness adjustment. Detailed statements are required for merged losses and for an overpayment carryforward going to a different FEIN.
Use the attachment checklist on page 4 to match each completed line to its required documents.
How to file
- Enter the tax year you are amending and identify your corporation in Step 1. Check the applicable change type and other relevant boxes.
- Enter previously reported or adjusted amounts in Column A and corrected amounts in Column B. Use whole dollars for dollar amounts.
- Explain the changes in the space provided. Attach a separate sheet if needed, along with the required supporting documents.
- Have an authorized officer sign and date the return and provide their title and phone number.
- If you owe tax on Line 68, complete Form IL-1120-X-V. Make your check or money order payable to Illinois Department of Revenue. Write your FEIN, tax year ending, and “IL-1120-X-V” on the payment. Attach the voucher and payment to page 1 and enter the payment amount in the space provided at the top.
Mail the return to:
Illinois Department of Revenue
P.O. Box 19016
Springfield, IL 62794-9016
Common mistakes
- Using the wrong version: This form cannot be used for tax years ending before December 31, 2024.
- Leaving out required attachments: The form warns that missing documents may result in disallowance of the corresponding line item.
- Completing Step 4 when it does not apply: If Line 23 is derived only inside Illinois and you are not a unitary filer, check Step 4, box A, and leave Lines 24 through 34 blank.
- Leaving Step 4 incomplete when it applies: If any portion of Line 23 is derived outside Illinois, or you are a unitary filer, check Step 4, box B, and complete all Step 4 lines. Do not leave Lines 28 through 30 blank.
- Entering negative sales amounts: Lines 28 and 29 cannot be negative. Round the apportionment factor on Line 30 to six decimal places.
- Omitting required information: The form warns that failure to provide required information could result in a penalty.
Questions people ask
Can I use this version to amend an older tax year?
Only if the tax year ends on or after December 31, 2024. The form says not to use it for tax years ending before that date.
What if I am filing only to report an increased net loss?
Check Step 1, box D, if you are filing only to report an increased net loss on Line 37, Column B.
What must I include for a federal change?
In Step 1, item P, check “Federal change,” select “Partial agreed” or “Finalized,” enter the finalization date, and attach your federal finalization.
Can I apply an overpayment to a future year instead of receiving it all as a refund?
Line 66 lets you enter the amount of the Line 65 overpayment to credit forward. Line 67 is the remaining refund amount. If the carryforward goes to a different FEIN, check the box on Line 66 and attach a detailed statement.
How will I know if additional penalty or interest is due?
The form says you will be sent a bill for any additional penalty and interest due.