According to Illinois Department of Revenue, 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.
If you are not required to file an Illinois tax return, you may want to do so in order to get a refund of the tax withheld.
You can start your Illinois non-resident return in TurboTax, and if you don't have a tax liability and don't want to file you can just delete the state return and not file.