If you moved to another state during the tax year, or if you work in a state that is different from the one in which you live, you might have to file tax returns in multiple states.
If you were a resident of one state and then became a resident of another, you'll need to file a part-year resident return for each state.
This type of return taxes all your income for the time you spent as a resident in the state. For example: In January you lived in New Jersey. As July rolled around, you permanently relocated to New York. You'd be required to file a part-year resident return for New Jersey on all the income you earned from January to July. For July to December, you'll file a part-year resident return for all the money you earned in New York.
Nonresident returns are used for taxpayers who earn money in any state other than the one in which they live.
For example: You live in New Jersey, but you are employed in New York. For the state of New Jersey, you'll file a resident return, which taxes all your income. You'll also have to file a nonresident return for New York, owing taxes on the income you earned in the state.
While it may seem like you are paying taxes on the same income twice, you're given the ability to claim a credit for the taxes paid to a nonresident state on your resident return.
If a state withholds any taxes from your salary, and it is not your home state, you must file a nonresident return to receive a refund of the money.