If you have IL income, you must file a nonresident tax return.
- a nonresident alien, you must 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, or federal Form 1040NR-EZ, U.S. Income Tax Return for Certain Nonresident Aliens With No Dependents.
https://tax.illinois.gov/individuals/filingrequirements.html#:~:text=a%20nonresident%20alien%2C%20yo....
