I was just checking back in, as I never saw you come into the chat, and on my end, it doesn't look my answer transferred in here.
Just in case, yes, non-residents are supposed to file a non-resident form in IL and pay taxes on Illinois source income.
Here's the website that explains: http://tax.illinois.gov/Individuals/FilingRequirements/
What they say is the following:
"If you were a nonresident, you must file Form IL-1040 and Schedule NR ifyou 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 either filed a Form IL-1023-C, Composite Income and Replacement Tax
Return, on your behalf or withheld enough Illinois Income Tax to pay your liability, you are not required to file a Form IL-1040.
[If you were] 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."
Hope this helps
(Positive feedback appreciated. That's how we're paid)
But, come back here if you have ANY questions on this.