Illinois Form IL-941-X, officially called the Amended Illinois Withholding Income Tax Return, is used by employers to correct errors previously reported on Form IL-941 (the quarterly Illinois Withholding Income Tax Return). This form allows you to make changes to previously filed withholding information—such as correcting wages, withholding amounts, overpayments, underpayments, or reporting additional employees or adjustments not included on the original return.
Employers file this form when they discover an error in a previously filed IL-941, such as overstating or understating withholding, omitting an employee, or incorrectly reporting a payment amount. Form IL-941-X ensures that your records with the Illinois Department of Revenue (IDOR) are corrected for the specific quarter affected. Filing must be done electronically via MyTax Illinois, unless you’ve been approved for a paper filing waiver. Paper filings must be mailed to the Illinois Department of Revenue, along with supporting forms such as Schedule P-X (Withholding Amount Payroll Schedule) and, if applicable, Schedule WC (Withholding Income Tax Credit).
Employers must submit a separate IL-941-X for each quarter being amended. Each submission corrects only one reporting period. Below, we’ll walk through how to file and then give clear, detailed, line-by-line instructions for completing every section of the form.
How To File Illinois Form IL-941-X
- When To File:
File Form IL-941-X as soon as you discover an error on a previously filed IL-941 or IL-941-X. Each amended return applies only to one quarter. - Where To File:
- Electronically (Preferred): Through MyTax Illinois or IDOR-approved tax software.
- By Mail (If Authorized):
Illinois Department of Revenue
PO Box 19052
Springfield, IL 62794-9052
- What To Include:
- Completed Form IL-941-X
- Attached Schedule P-X (to verify individual income and withholding corrections)
- Attached Schedule WC, if you’re applying withholding credits.
Do not attach separate correspondence or extra documents.
How to Complete Illinois Form IL-941-X
Step 1 – Provide Your Information
Federal Employer Identification Number (FEIN):
Enter your nine-digit FEIN exactly as it appears on your federal and Illinois registrations.
Sequence Number:
If applicable, provide your sequence number (used by payroll processors or IDOR). If not applicable, leave blank.
Business Name:
Write your legal business name.
C/O (In Care Of):
If another party (like a payroll provider or accountant) is handling this amendment, enter their name.
Mailing Address, City, State, ZIP:
Provide your full mailing address including suite or unit number, city, state, and ZIP code.
Check boxes:
- Check the box if your business name has changed.
- Check the box if your address has changed.
Reporting Period (Quarter):
Check one box to specify the quarter being amended:
- 1st Quarter: January–March
- 2nd Quarter: April–June
- 3rd Quarter: July–September
- 4th Quarter: October–December
Each return must correspond to one quarter only.
Step 2 – Tell Us About Your Business
A1. Total Number of Forms W-2 Issued:
Enter the total number of W-2 forms you issued for the entire year that report Illinois withholding. (Complete this only for your 4th quarter or final return.)
A2. Total Number of Forms 1099 Issued:
Enter the total number of 1099 forms reporting Illinois withholding issued for the year. (Also only required for the 4th quarter or final return.)
B. Permanently Stopped Withholding:
If your business has permanently ceased operations or no longer withholds Illinois income tax, check the box and enter the exact date you stopped withholding (MM/DD/YYYY). This will mark this return as your final submission.
Step 3 – Tell Us About The Amount Subject To Withholding
Line 1 – Corrected Amount Subject To Withholding:
Enter the corrected total dollar amount of compensation subject to Illinois withholding for the quarter.
This includes payroll, salaries, bonuses, commissions, or any other taxable payments that should have been reported for this period. Use your payroll records to determine the corrected total.
Step 4 – Tell Us About The Amount Withheld And Previous Overpayments
This section requires you to restate corrected withholding information for each month of the quarter, detailing the actual amounts withheld.
Line 2a – First Month of the Quarter
Enter the Illinois income tax withheld for each day wages were paid in the first month of the quarter:
- For Quarter 1: January
- For Quarter 2: April
- For Quarter 3: July
- For Quarter 4: October
Enter the daily withholding amounts in the day/amount columns. If no withholding occurred on a particular day, leave it blank.
At the bottom of Section 2a, add all daily entries and record the total withheld for that month.
Line 2b – Carry Forward
Enter the total amount from Line 2a here to carry the previous month’s total into this step.
Line 2c – Second Month of the Quarter
Use the same process for the second month of the quarter:
- For Quarter 1: February
- For Quarter 2: May
- For Quarter 3: August
- For Quarter 4: November
Record withholding per pay date and total all entries at the bottom.
Line 2d – Third Month of the Quarter
Follow the same procedure for the third month:
- For Quarter 1: March
- For Quarter 2: June
- For Quarter 3: September
- For Quarter 4: December
Add the total Illinois income tax withheld for the month on the “Total” line.
Line 2 – Total Withheld For The Quarter
Add Lines 2b, 2c, and 2d. Enter the combined total of all Illinois income tax withheld during the quarter.
If you are reducing withholding based on corrected W-2C forms, follow the IL-941-X instructions for documentation.
Line 3 – Previous Credits, Refunds, or IDOR-Approved Credits:
If your original return or a previously filed IL-941-X resulted in a credit, refund, or IDOR-approved overpayment for this period, enter that amount here.
Line 4 – Total Withholding Plus Credits:
Add Lines 2 and 3. This total represents your corrected total Illinois withholding and adjustments for the quarter.
Step 5 – Tell Us About Your Payments And Credits
Line 5 – Credit From Schedule WC:
If you are applying a credit from Schedule WC (Withholding Income Tax Credit), enter that amount here.
Line 6 – Total Payments Made To IDOR:
Enter the total amount of withholding payments you already made to the Illinois Department of Revenue for this period.
This includes all electronic and paper IL-501 payments. Do not estimate this figure — use your exact total from IDOR records or MyTax Illinois.
Line 7 – Total Payments And Credits:
Add Lines 5 and 6 to calculate your total payments and credits applied for this amended period.
Step 6 – Figure Your Balance
Line 8 – Balance Due:
If your total withholding (Line 4) exceeds your total payments and credits (Line 7), subtract Line 7 from Line 4. The result is your balance due.
You must pay this amount electronically or by check made payable to:
Illinois Department of Revenue
(Semi-weekly payers must pay electronically.)
Line 9 – Overpayment:
If your total payments and credits (Line 7) are greater than your total withholding (Line 4), subtract Line 4 from Line 7. The result is your overpayment. You can request that IDOR apply it as a credit or refund.
Step 7 – Sign Here
Under penalties of perjury, the authorized person must sign and date the return.
Provide:
- Signature
- Date (MM/DD/YYYY)
- Title
- Daytime phone number
If a paid preparer completed the form:
- They must sign and date the form.
- Include their name, PTIN, firm name, firm FEIN, firm address, and phone number.
- Check the box if the Department may discuss this return with the preparer.
- Mark the “Self-employed” box if applicable.
Schedule P-X – Withholding Amount Payroll Schedule
You must complete Schedule P-X and attach it to your IL-941-X.
Section A – Individual Corrections and Additions
List only those employees or payees whose income or withholding needs correction or were not included in the original IL-941 filing.
For each individual:
- Column A: Check the box verifying information has changed.
- Column B: Enter employee or payee name.
- Column C: Enter the Social Security number (no dashes).
- Column D: Enter corrected income for the quarter.
- Column E: Enter corrected withholding for the quarter.
Section B – Optional (For Paper Filers)
If you are filing a paper IL-941-X, you may use this section to list all remaining employees or payees not included in Section A.
Ensure the figures match those from your original IL-941 filing.
Include your Business Name, FEIN, and the Filing Period at the top of each page.
Important Filing Notes
- Always file one IL-941-X per quarter.
- Attach Schedule P-X (required) and Schedule WC (if claiming credit).
- Do not attach additional letters or documents.
- Keep a copy of all forms and supporting documents for your records.
- File electronically whenever possible to speed up processing and minimize errors.