Maricopa County, AZ, gained 696,000 residents between 2000 and 2006, the largest numerical increase of the nation's 3,141 counties, according to estimates released by the U.S. Census Bureau.
This increase surpasses the total population of all but 15 U.S. cities. Maricopa County, which includes Phoenix, has 3.8 million residents, making it the nation's fourth largest county.
The Census Bureau credits the dramatic increase in Maricopa County's population as the main reason Arizona became the nation's fastest-growing state between 2005 and 2006, adding nearly 3 million residents since the 1970 census.
Harris County, TX, had the second largest numeric increase between 2000 and 2006, at 486,000, and totaled 3.9 million. Riverside, CA (481,000); Los Angeles (429,000); and Clark, NV (402,000) rounded out the top five county gainers.
Among the 20 fastest-growing counties from 2000 to 2006, 13 were in the South, four in the West, and three in the Midwest.
Among the 10 counties that added the largest number of residents between 2000 and 2006, three were in Texas (Harris, Tarrant, and Collin), three in California (Riverside, Los Angeles, and San Bernardino), one in Georgia (Gwinnett, and one in Illinois (Will). Among the 20 counties with the largest numeric gains, 19 were in the South or West.
Los Angeles continued to be the most populous county in the nation with 9.9 million residents on July 1, 2006, followed by Cook, IL. (5.3 million); Harris, TX (3.9 million); and Maricopa (3.8 million).
Of those counties or county equivalents that experienced declining populations, Orleans Parish in Louisiana, which was hard-hit by Hurricane Katrina, had the largest population loss during the six-year period: 261,000. Orleans was followed by Wayne County, MI, which lost 89,000 residents, and Cook County, IL, with a population decline of 88,000. In 2006, Orleans Parish totaled 223,000 residents, while the population in Wayne and Cook declined to 2 million and 5.3 million, respectively.
Florida's Flagler, along the Atlantic Coast between Daytona Beach and Jacksonville, was the nation's fastest-growing county since Census 2000 with a 66.7 percent population increase from 2000 to 2006. The number of Flagler residents has reached 83,000.
Kendall, IL (61.7 percent), and Rockwall, TX (60.5 percent), were the second and third fastest-growing counties. Three of the 10 fastest-growing counties between 2000 and 2006 were in the Atlanta-Sandy Springs-Marietta, Ga., metropolitan area: Forsyth, ranking fifth with 53.4 percent growth; Henry, ranking eighth at 49.2 percent; and Paulding, ninth at 48.9 percent.