The schools are also adjusting to growth of up to 4 percent each year, said Terry Shoemaker, superintendent of the Wasatch County School District. The influx has included a large number of Spanish speakers, so the district has added an emphasis on English as a Second Language, Shoemaker said. However, the biggest challenge is recruiting and maintaining teachers who want to live in the area, he said.

"Teachers are excellent role models," he said. "We need to maintain stability in our teaching ranks."

Other Wasatch Front counties also showed strong growth.

Utah County gained 96,220 people since 2000, ranking it 36th nationally for numerical gain; and Salt Lake County saw an increase of 80,289 and ranked 42nd. Davis County also saw strong growth, with an influx of 37,265 people over six years, and Tooele grew by 12,817 over that period.

And, while Washington County was the only Utah county to make the nation's top 20 for six-year growth, Wasatch ranked 35th, Tooele ranked 40th, and Utah County ranked 84th.

Nationally, Los Angeles County remained the largest of the nation's 3,141 counties with a population of 9.9 million.

The fastest growing was Florida's Flagler County, which grew by two-thirds since 2000 to 83,000 people. The coastal county is located between Daytona Beach and Jacksonville.

Orleans Parish in Louisiana, hard-hit by Hurricane Katrina, lost 261,000 residents between 2000 and 2006. Meanwhile, 19 of the 20 counties that added the most people from 2000 to 2006 were in the South or West.

In the West, Maricopa County in Arizona saw the greatest population gain - 696,000 residents. The county, which includes Phoenix, had more than 3.8 million residents in 2006 and is key to Arizona's rank as fastest growing state, said Census Bureau Director Louis Kincannon in a statement.

"Maricopa's growth has been remarkable, adding nearly 3 million people since the 1970 census," said Kincannon.

For Utah, the total population estimated by the census is 65,000 fewer than the Utah Population Estimates Committee.

A large chunk of the lower estimate came from Salt Lake County, which is just shy of one million people according to UPEC. The census counts 978,701 living in the county.

"That's significant," Perlich said. "We've got counties that don't have (65,000) people. It's the equivalent of having missed Box Elder County and Carbon County combined."

Spendlove pointed out that in addition to Salt Lake County, Utah, Cache and Morgan Counties showed particularly low estimates.

In the past, some counties and cities have successfully challenged the estimates, and in 2001 Utah launched an unsuccessful challenge of its 2000 census count. Now the state is considering the first-ever state challenge to an annual census estimates, Spendlove said.

"We're trying to work within the Census Bureau to see if there is a way we can accomplish the same goal and correct these differences without a challenge," he said.

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E-mail: dbulkeley@desnews.com