The U.S. Census Bureau is the foremost agency for demographic information on U.S. citizens. The demographic information is compiled from the decennial census. This is a count of the entire population every ten years.
Helpful Links to Census and Demographic Data
Arizona Census Data - U.S. Census State QuickFacts
Maricopa County, AZ - U.S. Census County QuickFacts
Florida Census Data - U.S. Census State QuickFacts
Duval County, FL - U.S. Census County QuickFacts
Minnesota Census Data - U.S. Census State QuickFacts
Olmsted County, MN - U.S. Census County QuickFacts