Illinois has a state income tax that applies to most residents and workers

Yes, Illinois charges state income tax. The current rate is a flat 4.95 percent on all taxable income — meaning you pay the same percentage whether you earn $30,000 or $300,000 per year. This is different from the federal income tax system, which uses tax brackets that increase with income.

The state collects this tax from wages, self-employment income, rental income, investment gains, and other sources. If you work in Illinois or live there, you almost certainly owe it. The Illinois Department of Revenue administers the tax and processes returns filed through the standard tax season (January through April).

Illinois also taxes retirement income differently than many states do. Pensions and distributions from retirement accounts may be partially or fully exempt depending on your age and the type of account, but the rules are specific and worth understanding if you receive retirement payments.

Key Takeaways

  • Illinois state income tax is a flat 4.95 percent on all taxable income, with no brackets or variations based on how much you earn.
  • You owe Illinois income tax if you live in the state or work there, even if you live elsewhere and commute in.
  • Pensions and some retirement account distributions may be exempt or partially exempt, but the exemption depends on your age and account type.
  • You file Illinois state taxes separately from federal taxes using Form IL-1040, usually during the same filing season as your federal return.
  • Illinois does not have a local income tax, but some municipalities impose property tax at higher rates to compensate.

Who has to pay Illinois state income tax

You owe Illinois state income tax if you are a resident of the state or if you earned income while working in Illinois, even if you live outside the state. A resident is someone who lived in Illinois for more than six months of the tax year, or who maintained a permanent home there and spent more than 30 days in the state during the year.

Non-residents who worked in Illinois must report that income to the state, though you may be able to claim a credit on your home state's return to avoid double taxation. If you moved to or from Illinois during the year, you file as a part-year resident and report only the income earned during the months you lived there.

Students, military members, and people with temporary work visas have specific rules about residency status. If your situation is unusual — you moved mid-year, worked part of the year out of state, or received a large one-time payment — the Illinois Department of Revenue website has worksheets to help you determine your filing status.

What income is taxed and what is exempt

Illinois taxes wages, salaries, self-employment income, rental income, capital gains, and interest. The state also taxes income from partnerships, S-corporations, and other business structures. Most ordinary income sources are subject to the 4.95 percent rate with no deductions or adjustments.

Certain types of income are exempt from Illinois state tax. Pensions from public employee systems (teachers, police, firefighters, and other government workers) are fully exempt if you were a member before January 1, 2011. Pensions from private employers and IRAs are partially exempt: if you are 55 or older, you can exclude up to $20,000 of pension and retirement account income per year. Social Security benefits are also exempt.

Interest from U.S. Treasury bonds and certain municipal bonds is exempt. Disability payments and workers' compensation are exempt. Child support and alimony received are not taxed. If you received a large payment from one of these sources, you may not owe state tax on it even if you owe federal tax.

How to file Illinois state income tax

You file Illinois state taxes using Form IL-1040, which you can download from the Illinois Department of Revenue website or obtain by mail. You also need to file any required schedules — for example, Schedule C if you are self-employed, or Schedule IL-NR if you are a non-resident. The forms are filed separately from your federal return, though the filing deadline is usually the same: April 15.

You can file on paper by mail or file electronically through the state's online system or through tax software. The Illinois Department of Revenue does not operate its own e-file system; instead, you use commercial tax software (many offer free filing for lower-income residents) or work with a tax preparer. If you file electronically, you receive a confirmation number and can track your return status online.

If you cannot file by April 15, you can request an extension, which gives you until October 15 to file. An extension does not extend the time to pay taxes owed — you still owe payment by April 15 or you will face penalties and interest. If you expect a refund, filing early ensures you receive it sooner.

Estimated tax payments if you are self-employed or have other income

If you are self-employed, own a business, or receive income that is not subject to withholding (such as rental income or investment gains), you may need to make estimated tax payments to Illinois four times per year. These payments are due on April 15, June 15, September 15, and January 15 of the following year.

You calculate estimated payments based on your expected income for the year. If you underpay, you owe a penalty when you file your return, even if you ultimately owe no tax. If you overpay, the state refunds the difference or credits it to next year's taxes. Many self-employed people use tax software or work with a preparer to calculate the correct amount.

If your income varies significantly from year to year, you can base your estimated payments on your prior year's tax liability instead of your current year's income. This is often easier for people whose earnings are unpredictable.

State tax credits and deductions available to Illinois residents

Illinois offers fewer deductions and credits than the federal system. The state does not allow a standard deduction or itemized deductions like the federal return does. Instead, you report your total income and subtract only specific exemptions (such as pension exemptions or Social Security).

Illinois does offer a few targeted credits. The Earned Income Tax Credit (EITC) is available to lower-income working people and is calculated based on your federal EITC. The state also offers credits for property taxes paid, for child and dependent care expenses, and for contributions to certain savings programs. These credits are claimed on your state return using specific schedules.

If you paid taxes to another state on income you earned there, you may be able to claim a credit on your Illinois return to reduce double taxation. This is common for people who work in one state and live in another, or who moved during the year.

What happens if you do not file or pay on time

If you owe Illinois state tax and do not file by April 15, you face a failure-to-file penalty of 5 percent per month (up to 25 percent total) of the unpaid tax. If you file but do not pay, you face a failure-to-pay penalty of 0.5 percent per month (up to 25 percent total). Interest accrues on unpaid tax at a rate set by the state, currently around 8 percent per year, compounded daily.

If you owe a large amount and cannot pay in full, you can request a payment plan from the Illinois Department of Revenue. The state will work with you to set up monthly payments, though interest and penalties continue to accrue until the debt is paid. If you ignore the debt, the state can place a lien on your property, garnish your wages, or intercept your federal refund.

If you filed late or made an error on a prior year's return, you can file an amended return using Form IL-1040-X. You have three years from the original due date to file an amended return and claim a refund.

Frequently Asked Questions

Does Illinois tax retirement income differently than other states?

Yes. Pensions from public employee systems are fully exempt. Private pensions and retirement account distributions are partially exempt if you are 55 or older — you can exclude up to $20,000 per year. Social Security is fully exempt. Federal tax rules may differ, so you could owe federal tax on retirement income while owing little or no Illinois tax.

If I work in Illinois but live in another state, do I owe Illinois income tax?

Yes, you owe Illinois tax on income earned in the state. You file as a non-resident and report only the income from your Illinois job. Your home state may also tax that income, but you can usually claim a credit on your home state return to avoid paying tax twice on the same money.

What is the difference between Illinois state tax and federal income tax?

Illinois uses a flat 4.95 percent rate on all income, while federal tax uses brackets that increase with income. Illinois allows fewer deductions and exemptions than federal tax. You file both returns separately, and owing one does not affect the other, though some credits (like the EITC) are based on your federal return.

Can I file my Illinois taxes online?

Yes, you can file electronically through tax software or with a tax preparer. The Illinois Department of Revenue does not run its own e-file system, so you use third-party software. Many providers offer free filing for lower-income residents. You can also file on paper by mail.

What if I moved out of Illinois during the year?

You file as a part-year resident and report only the income earned during the months you lived in Illinois. You use Form IL-1040 and indicate your residency status. If you moved to a state with no income tax, you may owe Illinois tax on income earned before you left, but no tax on income earned after you moved.