All U.S. citizens are residents of at least one state for tax purposes. Your state of residence is determined by:

• Where you're registered to vote (or could be legally registered)
• Where you lived for most of the year
• Where your mail is delivered
• Which state issued your current driver's license 

You can be considered a resident of multiple states. It’s also possible to be considered a full-year resident of one state and a nonresident of another state, or a part-year resident in multiple states and nonresident in other states at the same time.

If you don't know which state you should consider your state of residence, contact a state to understand the resident guidelines.