Several Utah cities have successfully challenged their U.S. Census Bureau estimates of population as being too low.

Juliette Tennert, the state's top demographer, said it's crucial that census estimates are accurate because of population-based formulas for funding distributions — such as with state sales tax.

The state has long said the Census Bureau estimates may miss much of Utah's growth due to people moving to the state. The gaps between state and federal estimates had prompted the state to consider a first-ever challenge to the census estimates.

"The possibility of a statewide challenge is always there," Tennert said. "We are feeling more and more confident about the census getting better at estimating Utah's population."

In 2004, there was a gap of about 80,000 between state and federal estimates. In 2006, it had declined to 65,000, Tennert said. And upcoming revisions to the 2006 estimates could narrow that gap even more, she said.

The difference arises from the way migration in and out of a state is tracked. The Census Bureau relies primarily on federal income tax returns. The state uses a combination of federal income tax exemptions, housing data, school enrollment and membership in The Church of Jesus Christ of Latter-day Saints.

Cache County, along with all its cities, successfully challenged the Census Bureau's population estimate of 98,662, raising the county's population to 106,399, a 7.8 percent increase.

Cities that have successfully challenged are:

• Eagle Mountain, which raised its official population estimate from 12,232 to 17,391, a 42.2 percent increase.

• Saratoga Springs, which raised its estimated population from 7,283 to 10,750, an increase of 47.6 percent.

• Provo, which went from 113,984 to 116,217, an increase of 2 percent.

• West Valley City, which had its estimate rise by 0.3 percent, from 119,841 to 120,235.

• West Jordan, which had its estimate rise from 94,309 to 100,280, an increase of 6.3 percent.

• Bountiful, which boosted its estimate nearly 6 percent, from 41,161 to 43,576

Herriman has a challenge pending, Tennert said. However, since that challenge may have been submitted after the deadline, any changes could be folded into the city's 2007 estimate.

The state also has seen new incorporations this year. In Washington County, Apple Valley was incorporated with a July 1, 2006, population estimate of 582; Bryce Canyon City in Garfield County has a population of 138; Daniel in Wasatch County has a population of 726; and in Sevier County an annex added 390 people to Koosharem.

The Heber Valley area also could see a new city soon, as representatives of the proposed Aspen, Utah, have filed incorporation papers.

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E-mail: dbulkeley@desnews.com