According to the Wisconsin instructions:
A Resident is an individual that is domiciled in Wisconsin for the entire tax year.
A Nonresident is an individual that is not domiciled in Wisconsin at any time during the tax year.
A Part-Year Resident is an individual that is domiciled in Wisconsin for part of the tax year.
What if I am a resident and my spouse is not?
If you are married and one spouse is either a nonresident or part-year resident of Wisconsin in 2021 and the other spouse is a full-year resident of Wisconsin, the form to use depends on your filing status.
• If you file a joint Wisconsin income tax return, you must file Form 1NPR.
• If you file separate Wisconsin income tax returns, the nonresident or part-year resident spouse must file Form 1NPR; the full-year resident spouse must file Form 1 (individual income tax return for full-year
residents).
What is a domicile?
Your domicile is the permanent legal home you intend to use for an indefinite or unlimited period, and to which, when absent, you intend to return.
For more information: