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General Information

Who must file an Illinois tax return?

If you were

an Illinois resident, you must file Form IL-1040 if

  • you were required to file a federal income tax return, or 
  • you were not required to file a federal income tax return, but your Illinois base income from Line 9 is greater than your Illinois exemption allowance.

an Illinois resident who worked in Iowa, Kentucky, Michigan, or Wisconsin, you must file Form IL-1040 and include as Illinois income any compensation you received from an employer in these states. Compensation paid to Illinois residents working in these states is taxed by Illinois. Based on reciprocal agreements between Illinois and these states, these states do not tax the compensation of Illinois residents.

If your employer in any of these states withheld that state’s tax from your compensation, you may file the correct form with that state to claim a refund. You may not use tax withheld by an employer for these states as a credit on your Illinois return.

a retired Illinois resident who filed a federal return, you must file Form IL-1040. However, certain types of retirement income (e.g., pension, Social Security, railroad retirement, governmental deferred compensation) may be subtracted from your Illinois income. For more information, see the instructions for Line 5 and Publication 120, Retirement Income.

a part-year resident, you must file Form IL-1040 and Schedule NR, Nonresident and Part-Year Resident Computation of Illinois Tax, if

  • you earned income from any source while you were a resident, 
  • you earned income from Illinois sources while you were not a resident, or 
  • you want a refund of any Illinois Income Tax withheld.

a nonresident, you must file Form IL-1040 and Schedule NR if 

  • you earned enough taxable income from Illinois sources to have a tax liability (i.e., your Illinois base income from Schedule NR, Step 5, Line 46, is greater than your Illinois exemption allowance on Schedule NR, Step 5, Line 50), or
  • you want a refund of any Illinois Income Tax withheld in error. You must attach a letter of explanation from your employer.

Note: If you are a nonresident and your only income in Illinois is from one or more partnerships, S corporations, or trusts that withheld enough Illinois Income Tax to pay your liability, you are not required to file a Form IL-1040.

an Iowa, Kentucky, Michigan, or Wisconsin resident who worked in Illinois, you must file Form IL-1040 and Schedule NR if 

  • you received income in Illinois from sources other than wages, salaries, tips, and commissions, or 
  • you want a refund of any Illinois Income Tax withheld.

If you received wages, salaries, tips, and commissions from Illinois employers, you are not required to pay Illinois Income Tax on this income. This is based on reciprocal agreements between Illinois and these states.

The reciprocal agreements do not apply to any other income you might have received, such as Illinois lottery winnings and Illinois unemployment income.

an Illinois resident who was claimed as a dependent on your parents’ or another person’s return, you must file Form IL-1040 if 

  • your Illinois base income from Line 9 is greater than $2,425, or 
  • you want a refund of Illinois Income Tax withheld from your pay.

If your parent reported your interest and dividend income through federal Form 8814, Parents’ Election to Report Child’s Interest and Dividends, do not count that income in determining if you must file your own Form IL-1040.

the surviving spouse or representative of a deceased taxpayer who was required to file in Illinois, you must file any return required of that taxpayer.

a student, you are not exempt from tax nor are there special residency provisions for you. However, income, such as certain scholarships or fellowships, that is not taxable under federal income tax law, is also not taxed by Illinois.

a nonresident alien, you must file Form IL-1040 if your income is taxed under federal income tax law. Note: You must attach a copy of your federal Form 1040NR, U.S. Nonresident Alien Income Tax Return.

Note: Even if you are not required to file Form IL‑1040, you must file to get a refund of

  • Illinois Income Tax withheld from your pay,
  • estimated tax payments you made, or
  • withholding on income passed through to you by a partnership, S Corporation, or trust.

Who is an Illinois resident?

You are an Illinois resident if you were domiciled in Illinois for the entire tax year. Your domicile is the place where you reside and the place where you intend to return after temporary absences. Temporary absences may include duty in the U.S. Armed Forces, residence in a foreign country, out-of-state residence as a student, or out-of-state residence during the winter or summer.

If you filed a joint federal return and one spouse is an Illinois resident while the other spouse is a nonresident or a part-year resident, you may file separate Illinois returns. If you file a joint Illinois return, you will both be taxed as residents.

What is Illinois income?

Your Illinois income includes the adjusted gross income (AGI) amount figured on your federal return, plus any additional income that must be added to your AGI. Note: Some of your income may be subtracted when figuring your Illinois base income. For more information, see the Step-by-Step Instructions.

You should follow the federal law concerning passive activity income and losses. You are not allowed to refigure your federal passive activity losses.

Also, federal law will govern the taxation of income from community property sources in the case of spouses who file joint federal returns and who file separate Illinois returns.

How may I file?

File your individual income tax return electronically by using

  • MyTax Illinois, available on our website for free,
  • a tax professional, or
  • tax preparation software.

Almost all taxpayers can file electronically. Visit or see your tax professional. If you do not wish to file electronically, you may use the paper Form IL-1040.

When must I file?

Your Illinois filing period is the same as your federal filing period. We will assume that you are filing your Form IL-1040 for calendar year 2023 unless you are filing for a fiscal year and indicate a different filing period in the space provided at the top of the return. The due date for calendar year filers is April 15. If this date falls on a weekend or holiday, then the due date is the next business day after the weekend or holiday.

The due date to file and pay for 2023 is April 15, 2024.

We grant an automatic six-month extension of time to file your return. If you receive a federal extension of more than six months, you are automatically allowed that extension for Illinois. These extensions do not grant you an extension of time to pay any tax you owe. If you determine that you will owe tax, you must use Form IL-505-I, Automatic Extension Payment for Individuals, to pay any tax you owe to avoid penalty and interest on tax not paid by April 15, 2024.

The extended due date to file is October 15, 2024.

Should I round?

You must round cents to whole dollars on Form IL-1040 and most schedules, as directed. To round you must

  • drop amounts under 50 cents and
  • increase amounts of 50 to 99 cents to the next dollar.

For example, $1.49 becomes $1 and $2.50 becomes $3.

If you have to add two or more amounts to figure the amount to enter on a line, include cents when adding the amounts and round only the total.

Will I owe penalties and interest?

You will owe

  • a late-filing penalty if you do not file a return that we can process by the extended due date.
  • a late-payment penalty for tax not paid by the original due date of the return.
  • a late-payment penalty for underpayment of estimated tax if you were required to make estimated tax payments and failed to pay the required amount by the payment due dates.
  • a bad check penalty if your remittance is not honored by your financial institution.
  • a cost of collection fee if you do not pay the amount you owe within 30 days of the date printed on any IDOR-2-BILL, Final Notice of Tax Due for Form IL-1040, Individual Income Tax Return, you receive
  • a frivolous return penalty if you file a return that does not contain information necessary to figure the correct tax or shows a substantially incorrect tax, because you are taking a frivolous position or are trying to delay or interfere with collection of the tax.
  • interest on unpaid tax from the day after the original due date of your return through the date you pay the tax.

We will bill you for penalties and interest. For more information about penalties and interest, see Publication 103, Penalties and Interest for Illinois Taxes.

What if I cannot pay?

If you cannot pay the tax you owe but you can complete your return on time, file your return by the due date without the payment. This will prevent a late-filing penalty from being assessed. You will, however, owe a late-payment penalty and interest on any tax you owe after the original due date, even if you have an extension of time to file.

You have the option to pay the amount you owe electronically by using our website or by credit card. See the instructions for Line 40.

When must I file an amended return?

Do not file another Form IL-1040 to make changes to a previously filed Form IL-1040. You must file Form IL-1040-X, Amended Individual Income Tax Return, if

  • you discover that you made an error on your Illinois return after it was filed, or
  • your federal return has been adjusted either by the Internal Revenue Service (IRS) or on a federal Form 1040X, Amended U.S. Individual Income Tax Return, you filed; the change affects your Illinois income, additions, subtractions, exemptions, or credits; and the change is final.

Note: If the federal change results in a refund, do not file Form IL-1040-X until you receive notification that your change has been accepted by the IRS.

For more information, see Form IL-1040-X and Instructions.

What if I have household employees?

You may use Form IL-1040 to pay your household employees’ Illinois withholding. For more details on how to pay withholding for your employees, see the instructions for Line 20.

What if I change my address?

If you change your address after you file, visit our website or call us to tell us your new address and the date you moved.

What if I am an injured spouse?

If you are married and you filed a joint federal return with your spouse and you are an injured spouse (e.g., your spouse owes a liability, for which you are not responsible, to a government agency), you may elect to file separate Illinois returns using the “married filing separately” filing status. You may make this election up until the extended due date of your return, and once the election is made, it is irrevocable for the tax year.

Note: If you file a joint Illinois return, we may take the entire refund to pay your spouse’s liability.

What if I participated in a potentially abusive tax avoidance transaction?

If you participated in a reportable transaction, including a “listed transaction,” during this tax year and were required to disclose that to the IRS, you are also required to disclose that information to Illinois.

You must send us two copies of the form you used to disclose the transaction to the IRS. You must

  • attach one copy to your tax return, and
  • mail a second copy to the Illinois Department of Revenue,
    P.O. Box 19029, Springfield, Illinois 62794-9029.

Note: Employee benefit plans and other subtractions allowed on Form IL-1040, Lines 5 through 7, are not reportable transactions. For more information, contact the IRS or your tax professional.