St. Bernard and Orleans, two Louisiana parishes hit hard by Hurricane Katrina in 2005, were America’s fastest-growing counties in 2007, according to population estimates released today by the U.S. Census Bureau. St. Bernard — America’s fastest-losing county from 2005 to 2006 — experienced a 42.9 percent population increase between July 1, 2006, and July 1, 2007, increasing its population by almost 6,000. Orleans’ population rose by 13.8 percent, or nearly 29,000.

According to the estimates, all but one of America’s 10 fastest-growing counties were located in the South or West. Pinal, Arizona (near Phoenix) ranked third at 11.5 percent; Kendall, Illinois. (in the Chicago area) fourth at 10.6 percent; Rockwall, Texas (in the Dallas area) fifth at 8.2 percent; Flagler, Florida (between Daytona Beach and Jacksonville) sixth at 7.2 percent; and Union, North Carolina (near Charlotte) seventh at 7.2 percent. Finishing the list were three Georgia counties: Forsyth (7.2 percent), Paulding (6.7 percent) and Jackson (6.7 percent). Forsyth and Paulding are in the Atlanta metro area, with Jackson bordering on Athens-Clarke County.

Maricopa County, Arizona, home of Phoenix, was the top numerical gainer, increasing by 102,000 people between 2006 and 2007. Among the 10 counties that added the largest number of residents between 2006 and 2007, half were in Texas (Harris, Tarrant, Bexar, Collin and Travis), two in North Carolina (Wake and Mecklenburg), and one each in California (Riverside) and Nevada (Clark).

Los Angeles, California remained the most populous county, with a July 1, 2007, population of 9.9 million, a decline of 2,000 residents from 2006.

Other highlights for 2006-2007:

Seventy of the 100 fastest-growing counties were in the South, with 22 in the West and eight in the Midwest.

Among the 100 fastest-growing counties, more than one-third were in either Georgia (18) or Texas (16).

Texas was home to 11 counties among the 25 with the highest numerical gains. Each of the top 25 was in the South or West.