State Abbreviations

As a general rule, the names of states should be spelled out when they appear in sentences:

When the Oakies left Oklahoma and moved to California, it raised the I.Q. of both states.
(Will Rogers)

However, in bibliographies, lists, and mailing addresses, state names are usually abbreviated.

The two-letter, no-period state abbreviations recommended by the U.S. Postal Service (see Postal Abbreviations in the chart below) should always be used where a ZIP code follows. These postal (or ZIP code) abbreviations may also be used in any context where abbreviations are appropriate.

Some writers and editors still prefer to use the older forms of state abbreviations (see Traditional Abbreviations in the table below). If you follow this practice, be consistent in your use of the traditional abbreviations, and remember that eight states (Alaska, Hawaii, Idaho, Iowa, Maine, Ohio, Texas, and Utah) are only rarely abbreviated when using the older (pre-ZIP code) forms.

Finally, United States may be abbreviated to U.S. when used as an adjective, but it is customarily spelled out as a noun.