U.S. Department of Commerce, U.S. Census Bureau, Population Division
Population: Totals include resident population only. All years are based on a July 1 (midyear) estimate, except years that there is a Decennial Census count (2000 and 2010), in which case, those years are based on an April 1 count. The Decennial Census of Population uses mail and door-to-door collection of data whereas intercensal estimates are based on population redistribution factors and statistical modeling. The Decennial counts are more accurate and are used as the benchmark standards for intercensal counts.
Metropolitan statistical areas areas: Each Office of Management and Budget-defined metropolitan statistical area consists of one or more whole counties, and includes the counties containing the core urban area (a Census Bureau defined urbanized area), as well as any adjacent counties that have a high degree of social and economic integration (as measured by commuting to work) with the urban core. Areas are defined by the Office of Management and Budget as of February 2013.