Illinois & Michigan have tax reciprocity with regard to W-2 wages/salary. Reciprocity means that a MI resident working in IL is not liable for IL taxes on any W-2 income earned in IL. Such income is taxable only by his/her home state of Michigan.
Form IL-W-5-NR is used to advise an Illinois employer that you are a resident of MI, and therefore (due to reciprocity) your wages are not subject to Illinois withholding. Here's a link to the form:
https://www2.illinois.gov/rev/forms/withholding/Documents/currentyear/il-w-5-nr.pdf
If Illinois taxes were mistakenly withheld from your W-2 pay, you should submit a non-resident IL return, showing zero IL income, in order to receive a refund of those taxes. Your income is entirely taxable by your home state of MI.
Note that reciprocity applies only to W-2 wages or salary, not to any other type of income.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
