According to Montana Instructions for Form 2, you must file a Montana state income tax return if your federal gross income meets the threshold and you lived or earned income in Montana during the tax year.
What are Montana's filing thresholds?
If during the tax year you were a resident or part-year resident of Montana, or if you were a nonresident who received Montana source income; and you had a requirement to file a federal tax return, then you
must file a Montana income tax return. If you did not have a federal filing requirement, but have a
Montana addition or subtraction, you also must file a Montana income tax return.
Can I use a different filing status than my Federal tax return?
You must use the same filing status used on your federal tax return. Select the filing status you use on your federal Form 1040. If you do not have a federal filing requirement, use the filing status that you would use if you had a federal filing requirement.
What if I live in a reciprocal state?
Montana and North Dakota have a reciprocal agreement. If a Montana resident works or performs personal/professional services for an employer in North Dakota, the wages are treated as being earned in Montana and the Montana resident does not have to file a North Dakota income tax return reporting those wages.