NEW YORK (CNNMoney.com) -- St. George, Utah had the biggest gain in population in the United States during the past six years, according to a U.S. Census report released Tuesday.

The city in the southwestern corner of the state grew 31.6 percent to 118,885 between April 1, 2000 and July 1, 2005. St. George nosed out the former leader, the Greeley, Colorado metro area, which has gained 26.6 percent over the same period.

A metropolitan area is defined as one that has a core urban area and a population of 50,000 or more.

Most of the fastest growers were medium to smaller metro areas and six of the top 10 were located west of the Mississippi. Only one of the four eastern cities in the top 10 - Raleigh, North Carolina - was outside Florida.

In sheer numbers, Atlanta has added more people, 669,699, than any other metro area. It grew by 15.8 percent during the period. Other big gainers included Dallas (657,957), Riverside-San Bernardino (655,133) and Phoenix (613,201).

Quite a number of places lost population. Hinesville-Fort Stewart, Georgia decreased 4.6 percent, a greater rate than any other metro area. Numerically, the biggest loser was Pittsburgh, where the population dropped 45,013.

The Census Bureau also published stats for micropolitan areas, those with populations between 10,000 and 50,000. Palm Coast, Florida, is the fastest growing of these places; it gained 53.3 percent.

Losing the highest percentage of its population was Pecos, Texas, which dropped 11.4 percent.

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