Illinois & Michigan have tax reciprocity. That means that Illinois residents are not subject to Michigan income tax on their W-2 salary or wages.
You must file a non-resident Michigan tax return in order to claim a refund of the incorrectly withheld MI taxes. On that return you must allocate zero income to Michigan.
You should also file Michigan form MI-W4 with your Michigan employer, claiming exemption from MI withholding. Here's a link to that form:
https://www.michigan.gov/-/media/Project/Websites/taxes/Forms/MIW4.pdf?rev=3b636449ec174962a3afe0a39...
Your income is 100% taxable by your home state of Illinois. You must report ALL your income on your Illinois return.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
