Illinois Form IL-941 – Illinois Withholding Income Tax Return (2026)
Last reviewed: 2025-11-08
Use the Illinois Tax Form Calculator Form IL-941: Illinois Withholding Income Tax Return as a stand alone tax form calculator to quickly calculate specific amounts for your 2026 Illinois state tax return. Alternatively, you can use one of our Combined Federal and State Tax Estimators to quickly calculate your salary, tax, and take-home pay.
Form IL-941 is Illinois’s Quarterly Withholding Income Tax Return used by employers to report wages paid and income tax withheld from employee compensation. All employers with Illinois withholding obligations must file this return every quarter, even if no wages were paid or no tax was withheld. Electronic filing through MyTax Illinois is mandatory for most filers.
Who Must File Form IL-941
Employers, withholding agents, and payers who withhold Illinois income tax from wages, pensions, bonuses, or other compensation must file Form IL-941. This includes small businesses, corporations, and entities paying Illinois-based employees or nonresidents performing work within the state.
How to Complete Form IL-941
The form summarizes the quarter’s payroll activity and reconciles your Illinois withholding account. The 2025 form includes the following key lines:
- Line 1: Enter the total Illinois income tax withheld from employees during the quarter.
- Line 2: Enter adjustments or credits for previous quarters, if applicable.
- Line 3: Add Lines 1 and 2 to calculate total tax liability for this quarter.
- Line 4: Enter total Illinois withholding payments already made for this quarter.
- Line 5: Subtract Line 4 from Line 3 to determine the balance due or overpayment.
Employers should verify the quarterly total matches cumulative amounts reported on employee W-2 forms at year-end.
| Step 1 – Provide your information | ||
| Q | Reporting period — select quarter | |
| Step 2 – Tell us about your business | ||
| A1 | Total number of Forms W-2 with Illinois withholding (file only on 4th-quarter/final) | |
| A2 | Total number of Forms 1099 with Illinois withholding (file only on 4th-quarter/final) | |
| B | Final return? Enter date you stopped withholding (mm/dd/2026) | |
| Step 3 – Amount subject to withholding | ||
| 1 | Total dollar amount subject to Illinois withholding this quarter | |
| Step 4 – Amount withheld (enter daily amounts; monthly totals compute) | ||
| 2a | First month of quarter – Illinois Income Tax withheld (enter daily amounts 1–31) | |
| Total (add days 1–31) | ||
| 2b | Carry total from Line 2a | |
| 2c | Second month of quarter – Illinois Income Tax withheld (enter daily amounts 1–31) | |
| Total (add days 1–31) | ||
| 2d | Third month of quarter – Illinois Income Tax withheld (enter daily amounts 1–31) | |
| Total (add days 1–31) | ||
| 2 | Quarter total Illinois Income Tax actually withheld (Line 2b + Line 2c + Line 2d) | |
| Step 5 – Payments and credits | ||
| 3 | Credit from Schedule WC used this period | |
| 4 | Total withholding payments made to IDOR for this period (all IL-501) | |
| 5 | Total credits/payments (Line 3 + Line 4) | |
| Step 6 – Figure your balance | ||
| 6 | If Line 2 > Line 5, Line 2 − Line 5 = balance due. If Line 5 > Line 2, result is overpayment. | |
Example
Example: During Q1, an employer withheld $8,500 from all employee paychecks. No prior adjustments apply. Payments totaling $8,000 were remitted to IDOR during the quarter. On Form IL-941, Line 5 shows a balance due of $500 ($8,500 − $8,000).
Filing and Payment Deadlines
- Quarter 1: January–March → Due April 30
- Quarter 2: April–June → Due July 31
- Quarter 3: July–September → Due October 31
- Quarter 4: October–December → Due January 31
Timely filing prevents late-payment penalties. Employers can verify payments and liabilities through their MyTax Illinois dashboard.
Common Issues
- Forgetting to file when no wages were paid — Illinois still requires a zero return.
- Reporting discrepancies between IL-941 and annual W-2/IL-W-2 totals.
- Late deposits leading to automatic penalty notices from IDOR.
Last reviewed: 2025-11-08: If you believe this form requires an update, please contact us.
Related Forms and Resources
- Form IL-W-4 – Employee’s Withholding Allowance Certificate
- Form IL-W-4-NR – Nonresident Employee Withholding Certificate
- Form 941 – Federal Employer’s Quarterly Tax Return
- Official Illinois Form IL-941 (2026)
- Illinois Department of Revenue – IL-941 Guidance
Quick Access Tools
Frequently Asked Questions
Will IL tax my Roth conversions?
Conversions are taxable federally and typically flow to IL; IL retirement exclusion usually applies to distributions, not conversions—check IL guidance.
How do I amend my Illinois return?
File Form IL-1040-X after your original IL-1040 is processed; include revised schedules (e.g., Schedule ICR/CR/M) and explanations.
Why does Illinois distinguish pre-1969 and post-1969 gains?
Because Illinois enacted its income tax on August 1, 1969, any appreciation before that date occurred before the state had authority to tax income. Form IL-F preserves fairness by taxing only the gain realized since Illinois income tax law took effect. This approach avoids retroactive taxation while ensuring current gains are taxed appropriately.
When should Schedule FD be filed?
File Schedule FD with your annual IL-1040 return for the tax year in which the deferred income became federally taxable.
Why is Schedule M important for accurate Illinois taxes?
Illinois uses Schedule M to ensure fairness in applying its flat 4.95% tax rate. Because Illinois starts from federal AGI, this form ensures only Illinois-approved income is taxed and proper deductions are applied. It’s especially vital for retirees, military personnel, and taxpayers with multistate investments.
Important Notes
All calculations are estimates for guidance only. Always review your return and consider professional advice when submitting official filings.