FIPS county code
The FIPS county code is a five-digit Federal Information Processing Standard (FIPS) code (FIPS 6-4) which uniquely identifies counties and county equivalents in the United States, certain U.S. possessions, and certain freely associated states. The first two digits are the FIPS state code and the last three are the county code within the state or possession. On September 2, 2008, FIPS 6-4 was one of ten standards withdrawn by NIST as a Federal Information Processing Standard. FIPS 6-4 was replaced by INCITS 31:2009.
County FIPS codes in the United States are usually (with a few exceptions) in the same sequence as alphabetized county names within the state. They are usually (but not always) odd numbers, so that new or changed county names can be fit in their alphabetical sequence slot.
See also 
- Federal Register, September 2, 2008 (Volume 73, Number 170), page 51276
- http://www.nist.gov/itl/upload/FIPSCodesReplacementChart2012.pdf FIPS Codes Replacement Chart
Lists of state and county FIPS codes for the United States can also be found at:
- http://www.ers.usda.gov/Data/baseacres/Data/counties.xls, a Microsoft Excel spreadsheet (incomplete).