County
An administrative subdivision of a state used for local government, identified in postal data by a FIPS county code but not part of the mailing address itself.
In the United States, counties are the primary administrative division below the state level. There are 3,143 counties and county-equivalent entities (parishes in Louisiana, boroughs in Alaska, independent cities in Virginia). While the county is not printed on mail, it is a key attribute in ZIP code databases because a single ZIP code may span multiple counties.
Each county is identified by a 5-digit FIPS code (Federal Information Processing Standard): the first 2 digits are the state code and the last 3 are the county. For example, FIPS 06037 identifies Los Angeles County, California.
County information associated with ZIP codes is used in tax jurisdiction determination, insurance rating, congressional district mapping, and compliance with various regulatory requirements.