Here is Illinois' law:
As 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.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
