You must electronically file Form IL-941-X, Amended Illinois Withholding Income Tax Return, with all required support, if
- you need to correct amounts you reported on previously filed Forms IL-941 or IL-941-X,
- you disagree with a change we made on your account, or
- you are requesting approval of an overpayment for a refund.
If you made an error that requires a Form IL-941-X and you made the same reporting error on your return and your employee’s Form W-2 or payee’s Form 1099 or W-2G, you must also provide your employee or payee with a Form W-2c or corrected Form 1099 or W-2G, and attach copies to your Form IL-941-X. We encourage you to use
MyTax Illinois to file and submit this form electronically.