Spendlove said while the federal numbers for 2005 aren't out yet, the state's population estimates have been higher than the Census Bureau's in the past.

Utah County and several cities in the county successfully challenged the Census Bureau's 2004 population estimates, raising the county's estimated population from 403,000 to 429,000. That's still about 2 percent lower than UPEC's estimates for the county.

Spendlove said Utah County is a more extreme example, but the statewide gap between federal and state population estimates has been widening slightly since 2001.

The state and census both use federal tax returns, along with birth and death certificates, to come up with estimates, he said. The state also uses other information such as school enrollment, LDS Church records and housing growth.

While the Utah estimates have shown strong net in-migration since 2000, the census estimates have shown that while Utah is gaining about 10,000 international migrants each year, it's also showing internally more people moving out of Utah than into the state.

"We don't know exactly what the decennial census will come up with," Spendlove said. "I feel very confident in the methods the Population Estimates Committee uses. . . . It's made up of local and state experts who know about what's happening with the population, what's happening on the ground."

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