It depends - If you move states in a prior year, you will only need to file a resident state income tax return during the current tax year.

So in your situation, if you were a resident of MT for the entire 2017 calendar year, you would report all income from all sourced (include an ND 401(k) distribution) on your MT resident state income tax return. The federal government has determined that retirement income is only taxed in your state of residency at the time the distribution was received (regardless of where the original 401(k) account was setup and funded). This is why you are being asked questions about a retirement distribution from an ND 401(k) account that was received while you were a resident of MT.