With a one-year growth rate of 2.4 percent, Utah is the sixth-fastest-growing state, with a population of 2.55 million, according to estimates released today by the U.S. Census Bureau.

Utah's population still exceeds Nevada's, but barely, according to the estimates, which show Nevada's population at just under 2.5 million. And Arizona has surpassed Nevada as the nation's fastest-growing state with a growth rate of 3.6 percent.

"What the data shows to me is Utah continues to be one of the fastest-growing states in the nation," said Robert Spendlove, the state's top demographer. "We've been in the top 10 for the past several years. ... Utah is at the center of a dynamic area of the country."

However, Spendlove and other demographers believe the Census Bureau is undercounting Utah's population by about 65,000 people.

The Utah Population Estimates Committee contends the state's population broke 2.6 million people this year, with a growth rate of 2.7 percent, said Spendlove, manager of demographic and economic analysis for the Governor's Office of Planning and Budget.

The state now has six months to decide whether to become the first state to officially challenge the census estimates, Spendlove said. He is encouraged that the population gap between state and federal estimates has lowered from 3.2 percent last year to 2.6 percent this year.

"They are still different, but the difference has narrowed," Spendlove said. "One of the reasons it has narrowed ... is migration is much closer to what we think migration should be for the year 2006."

It's important for the census estimates to be accurate, in part because they're tied to federal funding in areas such as transportation and health care, Spendlove said.

If there is a disagreement about the population count, it's common for cities and counties to submit challenges, but Spendlove said it is difficult for small areas, and yearly local challenges can become tedious.

"The theory is that if the state can essentially act in the interest of all areas within the state to ensure all the estimates are the best they can be, it would take the burden off some of our local areas," Spendlove said.

Provo has spent about 40 work hours on three successful challenges to its census estimates, said Gary McGinn, director of community development for Provo.

The city would appreciate the help from the state but would still want to make sure it agrees with the state estimates, he said.

"An accurate picture of what's happening in your city... is invaluable to have," he said. "It really does affect the distribution of tax moneys."

The growth estimates released Friday are based on state estimates for 2005 that were revised after several Utah cities challenged their census estimates. The 2005 estimate was boosted by more than 20,000 people to 2.49 million.