Wisconsin does have a state income tax, and if as a resident or nonresident you made more than a certain amount of money in Wisconsin, you'll need to file a return. In some cases, if your withholding won't cover how much you owe in state tax, you may also need to file and pay quarterly estimated tax payments throughout the year.
TL;DR (Too Long; Didn't Read)
If you have earned an income in the state of Wisconsin during the year, you will most likely need to file a state tax return. Any part-time resident earning more than $2,000 in gross income during the year must file a state tax return.
Wisconsin Resident Filing Requirements
If you're a Wisconsin resident, whether or not you are required to file a tax return depends on how much money you've made. Your income includes gross income before deducting any expenses, but excludes items that are exempt from Wisconsin income tax, such as Social Security benefits and interest paid by the federal government.
The exact cutoffs depend on your age and filing status. If you're under 65 and single, for example, you are required to file if you've made $11,080 or more, but if you're a married couple filing jointly with both spouses at least age 65, you're required to file if you've made $21,110 or more. You can look up the specific filing requirements for the current year on the Wisconsin Department of Revenue website.
If you or your spouse is eligible to be claimed as someone's dependent, different filing requirements apply. In that case, if you have at least $1,050 in income, including at least $351 in non-wage income, such as interest, taxable scholarships and dividends, you must file. Otherwise, a separate, lower set of threshold numbers apply for each filing status.
Additionally, if you owe a withdrawal penalty to Wisconsin for an IRA or other retirement plan, health savings account or Coverdell education savings account, you must file a return regardless of how much money you made.
Nonresident Filing Requirements
If you're not a Wisconsin resident or only a part-year resident, different filing requirements apply. In that case, you generally must file if your Wisconsin gross income, before expenses, was $2,000 or more. For married couples filing either jointly or separately, that applies to the combined income of the two spouses.
Like many other states and the federal government, Wisconsin may require you to file and pay quarterly estimated tax payments if your withholdings won't cover your tax liability.
Generally, you must file and pay estimated tax if you expect to owe at least $500 in tax after withholding and credits, and your withholding will be less than the smaller of 90 percent of your tax or 100 percent of your previous year's tax. If you were a resident of Wisconsin for all of the previous tax year and owed no tax that year, you're not required to pay estimated tax.