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

Illinois charges a flat income tax rate of 4.95 percent on wages, retirement income, and other earnings. This rate applies to all residents and anyone who works in the state, regardless of income level. The tax is withheld from paychecks by employers, similar to federal income tax.

Unlike the federal system, Illinois does not use tax brackets—everyone pays the same percentage. This means a person earning $30,000 per year and a person earning $300,000 per year both pay 4.95 percent on their taxable income. The state also taxes certain types of investment income, though long-term capital gains have different treatment under current law.

Key Takeaways

  • Illinois residents and workers pay a flat 4.95 percent state income tax on wages and most other income.
  • Your employer withholds state income tax from your paycheck, just as they do for federal tax.
  • You file an Illinois state tax return (Form IL-1040) by the same important date as your federal return, usually April 15.
  • Certain income types, such as Social Security benefits and some retirement distributions, are exempt from Illinois state tax.
  • If too much tax was withheld during the year, you receive a refund when you file your return.

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. Residents include people who live in Illinois for the entire year, as well as people who moved into or out of the state during the year. If you worked in Illinois but lived in another state, you still owe Illinois tax on the income you earned here.

Some types of income are exempt. Social Security benefits are not taxed by Illinois. Distributions from certain retirement accounts, including traditional IRAs and 401(k) plans, are also exempt from state tax. Military pensions and some other government pensions receive special treatment as well. If you are unsure whether a specific income source is taxed, the Illinois Department of Revenue website lists the full rules.

How Illinois state tax is withheld from your paycheck

When you start a job in Illinois, you complete a state withholding form (similar to the federal W-4) that tells your employer how much state tax to take out of each paycheck. Your employer then sends that money to the Illinois Department of Revenue on your behalf. The amount withheld depends on your income level and the withholding choices you make on the form.

If you have multiple jobs, work as a contractor, or have other income sources, you may need to adjust your withholding or make estimated tax payments. Underwitholding can result in owing money when you file your return. Overwitholding means you will receive a refund. You can change your withholding at any time by submitting a new form to your employer.

Filing your Illinois state tax return

You file your Illinois state return using Form IL-1040, which is due on the same date as your federal return—usually April 15. You can file by mail or electronically through the Illinois Department of Revenue website or through tax software. If you file your federal return electronically, you can file your state return the same way.

To file, you will need your W-2 forms from your employer, records of any 1099 income, and documentation of deductions or credits you claim. Illinois allows you to claim the standard deduction or itemize deductions, just as you do on your federal return. If you owe money, you can pay when you file or set up a payment plan with the state.

Illinois tax credits and deductions you may use

Illinois offers several tax credits that can reduce the amount of tax you owe. The Earned Income Tax Credit (EITC) is available to low- and moderate-income workers and is calculated based on your federal EITC. The state also offers credits for property taxes paid, child care expenses, and other situations. Credits directly reduce your tax bill, making them more valuable than deductions.

You can also deduct certain expenses from your income before calculating tax owed. The standard deduction for Illinois is set each year and varies by filing status. If your itemized deductions exceed the standard deduction, you can itemize instead. Common itemized deductions include mortgage interest, charitable contributions, and state and local taxes (subject to federal limits).

What happens if you do not file or pay on time

If you miss the April 15 important date, the Illinois Department of Revenue charges penalties and interest on any unpaid tax. The penalty for filing late is typically 5 percent of the unpaid tax per month, up to a maximum. Interest accrues daily on the unpaid balance. If you cannot pay by the important date, filing your return on time and paying what you can reduces the penalties.

If you owe money and do not pay, the state can place a lien on your property, garnish your wages, or intercept your tax refund. If you are unable to pay the full amount, you can request a payment plan or an offer in compromise (a settlement for less than you owe). Contact the Illinois Department of Revenue to discuss your options before the debt grows.

Frequently Asked Questions

Do I have to file an Illinois state return if I did not earn much income?

You must file if your income exceeds the filing threshold for your age and filing status. The threshold varies each year. Even if you are not required to file, you should file if you had tax withheld, because you may receive a refund. Contact the Illinois Department of Revenue or check their website for the current year's threshold.

Can I deduct federal income tax from my Illinois state tax?

Yes, if you itemize deductions on your federal return. State and local taxes (SALT) are deductible on your federal return up to $10,000 per year. However, on your Illinois state return, you cannot deduct federal income tax because Illinois does not allow that deduction. You can deduct state and local property taxes and sales taxes on your federal return.

What if I moved out of Illinois during the year?

You are a part-year resident and owe Illinois tax only on income earned while you lived in the state. You will file both an Illinois return (for the months you lived there) and a return in your new state (for the months you lived there). Each state taxes only the income earned within its borders during the time you were a resident.

Is there a penalty if my employer did not withhold enough state tax?

No penalty applies to you if your employer made a mistake. However, you will owe the unpaid tax when you file your return. If a large amount was not withheld, you may owe a penalty on the underpayment itself. To avoid this in the future, verify that your withholding is correct by reviewing your pay stub or using the Illinois Department of Revenue's withholding calculator.

Can I file my Illinois return before I receive my W-2?

You can file once you have all the documents you need, including your W-2. If your employer is late sending your W-2, you can request a transcript from them or contact the IRS. You do not have to wait until the last minute—filing early can speed up your refund if you are owed one.