The population data for come from three sources. Population counts for 1990 are from the 1990 decennial census (SF1 files). The population counts for 2000 are from the U.S. Census Bureau's population estimates program (http://www.census.gov/popest/). Those estimates are the April 1, 2000, base for the vintage 2009 county population estimates, which may differ slightly from the 2000 decennial census counts because of post-enumeration corrections. The 2014 population counts are from the U.S. Census Bureau's population estimates and are as of July 1 of that year.