As defined in Chapter 1 of Title 23, the 50 States comprising the United States, plus the District of Columbia, and the Commonwealth of Puerto Rico. However, for the purposes of some programs (e.g., Sections 18, 16, and RTAP) the term may also include territories (Virgin Islands, Guam, American Samoa, and the Northern Mariana Islands).
Do not abbreviate U.S. states.
Always spell out the names of states and territories when standing on their own, and unless it's a list or mailing address, it's preferable to spell out state names even when followed by a city, (but use Washington, D.C.). When abbreviated, it's preferable to use the long abbreviation, e.g., Calif., Colo. (see Chicago 14.17), except when used in a mailing address (CA, CO, DC).