The AP Stylebook says state abbreviations are used in both datelines and in text.
Of course, use state abbreviations in conjunction with the name of a city, town, village or military base in most datelines. However, there are exceptions for large cities that stand alone in datelines.
Also use state abbreviations in conjunction with the name of a city, county, town, village or military base in text. (i.e. He went from Chicago, Ill., to Austin, Texas.)
Finally, use state abbreviations in short-form listings of party affiliations: D-Ala., R-Mont.
AP Stylebook: State abbreviations
Ala. Ariz. Ark. Calif. Colo. Conn.
Del. Fla. Ga. Ill. Ind. Kan. Ky.
La. Md. Mass. Mich. Minn.
Miss. Mo. Mont. Neb. Nev.
N.H. N.J. N.M. N.Y. N.C. N.D.
Okla. Ore. Pa. R.I. S.C. S.D.
Tenn. Vt. Va. Wash. W.Va. Wis. Wyo.
- In headlines, don't use periods for state abbreviated with two capital letters: NY, NJ, NH, NM, NC, SC, ND, SD AND RI. Other states retain periods: Ga., Ky., Mont., Conn.
- Use state of Washington or Washington state when necessary to distinguish the state from the District of Columbia. (Washington State is the name of a university in the state of Washington.)