US county GEOID
The five-digit geographic identifier of a US county, composed by the Census Bureau from the state and county codes.
Five digits: the two-digit state followed by the three-digit county. Abbeville County, South Carolina is 45001, where 45 is South Carolina and 001 the county within it.
Unlike the bare US county FIPS code, this form is unique across the whole country, which makes it the safer of the two to store and to join on.
Leading zeros are significant at both ends: 01001 is Autauga County, Alabama, and read as a number it is no longer a county code at all.
