Remember that America is more than just the United States. A number of countries comprise North, Central, and South America. When you mean the United States of America, use United States instead of just America. Be as specific as possible in your references to countries and their citizens. When abbreviating the United States, use U.S. (with periods). USA, however, when used has no periods.
When a state name is used in text with a town but no street address, it is spelled out.
When a state name is used as part of a mailing address, use the two-letter post office abbreviation.
Do not use the two-letter post office abbreviations in lists, tables, notes, bibliographies, or indexes. For the correct abbreviations to use in these cases, see section 14.17 of the Chicago Manual.
Spell out when used as a noun; abbreviate when used as an adjective.
Use of comma with state names
Use a comma before and after a state name when it's used with a town or city name in text.