Illinois has a flat tax of 5% on federal AGI wages.

Social Security benefits are not taxed by the state of Illinois.

Other Retirement Income and exemptions;

If you receive a distribution from a qualified retirement plan, such as a 401(k), IRA, self-employment retirement, traditional IRAs that have been moved to Roth IRAs, U.S. Retirement bonds that have been redeemed, deferred pensions from state and local government service, disability and retirement plans from the government and military plans you are exempt from state taxes.

Do I have to file a return?

If you are an Illinois resident you must file a Form IL-1040 under the conditions that you are required to file a federal income tax return or if you are not required to file a federal income tax return you Illinois income from Line 9 on IL-1040 is greater than your state exemption.

Any Illinois residents who earned income in Iowa, Kentucky, Michigan or Wisconsin must file a Form IL-1040, any income earned in those states must be included on this form. If you were paid in one of the previously mentioned states not all wages are taxed by the state of Illinois. Based on a reciprocal agreement with those state they should not levy state taxes for residents of Illinois.