Click on 'File a Return" in the Withholding account box. 2. Navigate to the appropriate filing period to file a return (Forms IL-941 and IL-941-X). 3.You must complete every step to report changes previously reported on your Forms IL-941 or IL-941-X. If you discontinue having Illinois employees or payees, complete IL-941, Step 2, Line B, for your final reporting period. When is my Form IL-941 return due? Who must file Form IL-941-X? Who needs to fill out Form IL-941-X? Employers and businesses who have reported incorrect tax amounts or need verifications are required to fill out this form. Overpayment as a nonemployee, file Form 941 for each delinquent quarter.