County codes by state are accessible through the FIPS information database available from the U.S. Census Bureau. The bureau publishes this file each time new data about state and county geography is released.
U.S. county codes are five-digit numerical arrangements that denote the state and county of a geographical area. The American National Standards Institute manages and distributes codes as a standard method of identifying counties and county equivalents within the United States.
The first two digits of the FIPS code designate the state containing the county in question, and the last three designate the county. States are numbered in order alphabetically, and except for a few exceptions, counties are ordered alphabetically within their respective states. For example, as of the Census Bureau's 2010 code release, Alabama's Autauga County has the FIPS code 01003 and Baldwin County has the FIPS code 01003. The digits that designate the counties are usually separated with one digit between them so that if a county is added, it can occupy its correct place in alphabetical order.
FIPS stands for the Federal Information Processing Standard, used throughout the United States. In addition to being used to categorize geographical areas, FIPS codes are used in emergency alert and weather transmissions as a way to simply communicate affected locations.