Source: U.S. Census Bureau, 1990 and 2000 Censuses of Population (corrected), and 2007 county estimate files.
1) The FIPS codes uniquely identify each county and are part of the Federal Information Processing Standards (FIPS) developed by the National Institute of Standards and Technology (NIST), U.S. Department of Commerce. For more information, see the NIST FIPS publication page.
2) The 2003 rural-urban continuum codes classify metropolitan counties (codes 1 through 3) by size of the Metropolitan Statistical Area (MSA), and nonmetropolitan counties (codes 4 through 9) by degree of urbanization and proximity to metro areas. See rural-urban continuum codes for precise definitions of each code.