According to Illinois Instructions for Form IL1040, there are certain stipulations that will require you to file an Illinois tax return.
Illinois Residents
You must file an Illinois tax return if:
- You were required to file a federal return, or
- You were not required to file a federal return but your Illinois income exceeds your exemption allowance.
If you are an Illinois resident and worked in Iowa, Kentucky, Michigan or Wisconsin:
- You must file 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.
If you are a retired Illinois resident:
If you filed a federal return, you must file an Illinois tax return, however, certain types of retirement income may be subtracted from your Illinois income.
Illinois Part Year Residents
As an Illinois part-year resident, you are required to file an Illinois return 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.
Illinois Nonresidents
As an Illinois nonresident, you must file an Illinois return if:
- You earned enough taxable income from Illinois to have a tax liability.
- You want a refund of any tax withheld in error for Illinois.
What if I live in a reciprocal State?
If you lived in Iowa, Kentucky, Wisconsin, or Michigan and worked in Illinois you must file an Illinois tax return if:
- You received income from sources other than wages, salaries and tips.
- You want a refund of any Illinois 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.
What if someone can claim me as a dependent?
If you are an Illinois Resident who was claimed as a dependent on another person’s return, file a return if:
- Your Illinois base income is greater than $2,425 or
- You want a refund of Illinois tax withheld.
Other special circumstances
If you are 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. Please refer to the special instructions on how to file for a deceased taxpayer.
If you are a nonresident alien, file Form IL-1040 if your income is taxed under federal income tax law. You must attach a copy of your federal Form 1040NR, U.S. Nonresident Alien Income Tax Return.
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.
Do I need to file using the same filing status as my Federal return?
Generally, you should use the same filing status as what is listed on your federal return. However, there are a few exceptions:
- If you file a joint federal return and you are an injured spouse (your spouse owes a liability, for which you are not responsible, to a government agency), you should file separate Illinois returns using the “married filing separately” filing status.
- If you file a joint federal return and one spouse is a full-year Illinois resident while the other is a part-year resident or a nonresident (e.g., military personnel), you may choose to file “married filing separately.”
If you are in a civil union, you must file your Illinois return using the same filing status as on your federal return.