US Census definitions of a Geography and FIPS CODES
The FIPS county code is a five-digit Federal Information Processing Standards (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.
See Attachment
A 15-digit number that begins with the state identifier and ends with the block identifier.
BLOCKID: 15-character code that is the concatenation of fields consisting of the 2-character state FIPS code, the 3-character county FIPS code, the 6-character census tract code, and the 4-character tabulation block code.