Some abbreviations of state names are Colo. or CO for Colorado and Del. or DEL for Delaware. There are two types of state abbreviations, standard abbreviations and postal abbreviations. While all postal abbreviations are two letters without punctuation, standard abbreviations vary in length and end with a period.
For example, the standard abbreviation for Alabama is Ala., and the postal abbreviation is AL. Alaska has no standard abbreviation, but the postal abbreviation is AK. Arkansas is abbreviated Ark. or AR, and Arizona is abbreviated Ariz. or AZ. California and Connecticut are abbreviated Calif. or CA, and Conn. or CT, respectively. Besides Alaska, other states that have no standard abbreviation are Hawaii, Idaho, Iowa, Maine, Ohio and Utah.
In addition to the 50 states, U.S. districts, territories and possessions are abbreviated as well. For example, the District of Columbia is abbreviated D.C. or DC. American Samoa has no standard abbreviation, but the postal abbreviation is AS. The postal abbreviation for the Marshall Islands and Northern Mariana Islands are MH and MP respectively. Puerto Rico, a commonwealth of the United States, is abbreviated P.R. or PR.
Prior to 1963, the United States Postal Service encouraged customers to used the standard abbreviation or the full state name in all correspondence. However, when the Postal Service introduced the Zip code system on July 1, 1963, it issued new, two-letter abbreviations to make room for the Zip Code after the city and state.