addresses

Use U.S. Postal Service abbreviations (such as CO for Colorado and DC for District of Columbia) for states in bibliographies, references, and full addresses (those that include streets or post office boxes).

In text, when you refer to a state with a city or by itself (for example, "The state energy office is stepping up solar retrofit activities in Massachusetts."), spell out the name of the state in full, except for the District of Columbia (D.C.). See also states and countries.