How do I know if I am a resident, part-year resident, or nonresident of a state?

Residency rules vary by state, so it's best to check with your Department of Revenue if you are unsure about your state residency status. In the meantime, you can use the following definitions as a general guide.
However: If you are enlisted in the military and stationed in another state, you are considered a resident of the state you enlisted in (your state of record with the military). You would file a resident tax return in your state of record unless you also have non-military income in the state you are stationed in. See Military Spouse Residency Relief Act and State Taxes.

Resident

You are a resident of a state if that’s where your main home is located for the entire tax year. It’s the state where you intend to live when you return from a vacation, business trip, school, etc.
Example 1 – You have a home in Idaho where you live most of the year. Every December, you drive your RV to Arizona, returning to Idaho in March or April. You are an Idaho resident.
Example 2 – You're currently attending the University of Minnesota. Before that, you lived with your family in Indiana. After you graduate, you plan to move back to Indiana. You are an Indiana resident.

Nonresident

For tax purposes, you are a nonresident of a state if you temporarily lived there (with no intention of making it your home) or didn't live there during the tax year and received income from that state because you:

• Worked there;
• Received income from sources located in that state, such as rental property;
• Received income from sources located in that state as a beneficiary of an estate or trust.

Tip: Prepare your nonresident state return(s) first, then any part-year resident state returns. Prepare your resident state last. This allows any credits or deductions for taxes already paid in your nonresident states to be used in your resident state's return.

Example 1 – You live in Colorado and worked on a road construction crew in New Mexico for several weeks. You'll need to file a New Mexico nonresident return (in addition to your normal Colorado resident return) so you can report your New Mexico earnings to the state of New Mexico.
Example 2 – You live in Oregon and have a rental property in California. You'll need to file a California nonresident return (in addition to your normal Oregon resident return) so you can report your rental income to California.
Example 3 – You live in New York and your great uncle dies. His Connecticut farm continues to operate until it can be sold. You are a beneficiary of the farm. You’ll need to file a Connecticut nonresident return (in addition to your normal New York resident return) so you can report your beneficiary income to Connecticut.
Example 4 – You live in Kentucky and receive interest from a bank in Rhode Island. In this case, you do not need to file a nonresident Rhode Island return because the source of the income is money made from money (not money made from sales, workers, or property located in that state).
For more information, click How Do I file a Non-Resident State Tax Return.

Part-year Resident

You are a part-year resident of a state if your main home was located there for a portion of the tax year. Taxpayers who relocate from one state to a new state will often be part-year residents of both states.
Example – You moved from Arkansas to Georgia during the tax year. Georgia is your new home and you do not intend to return to Arkansas in the foreseeable future. For the tax year, you are considered a part-year resident of both Arkansas and Georgia and will file part-year returns in both states. If all of your income is from Georgia next year, you'll just file a Georgia Resident tax return.
For more information, see I Moved to Another State During the Year, and More info about filing part-year resident tax returns
http://gengwg.blogspot.com/