I was renting a home in Illinois. I bought a home in Wisconsin on 12/18. do I need to fill in both states???

You only need to file a return for a particular state if your income is sufficient to reach the threshold. You will need to indicate that you are a part-year resident for both IL (and WI if required to file).

Must I file a Wisconsin income tax return?

If you are a nonresident or part-year resident of Wisconsin and your Wisconsin gross income (or the combined gross income of you and your spouse) is $2,000 or more, you must file a Form 1NPR, Nonresident and Part-Year Resident Income Tax Return. The Form 1NPR and instructions can be downloaded from our website​.

Gross income means all income (before deducting expenses) reportable to Wisconsin which you received in the form of money, property, or services. It does not include items that are exempt from Wisconsin income tax, such as U.S. government interest.

• For additional filing requirements, please see page 4 of the Form 1NPR instructions.