Keeping track of the area's booming population takes a lot of time and can be confusing for the outside observer, since the city's numbers have been diverging wildly from estimates released by the U.S. Census Bureau.

The Census Bureau put Las Vegas' 2006 population at 552,500 -- not enough to crack the top 25 cities by population in 2006.

"Any high-growth city tends to be undercounted," said Richard Wassmuth, a statistical analyst for Las Vegas. The discrepancy in 2006 was "about 39,000, so we're getting up around a 6 or 7 percent difference now."

Las Vegas calculated its estimate using dwelling unit statistics, an occupancy survey conducted each year by the U.S. Post Office and average household size.

The postal occupancy survey is unique to Clark County, Wassmuth said.

"We have such growth, we pay the postal service to do that every year," he said. "We have the most updated information."

Tracking the city's population takes a lot of work, but the information is used for planning and funding decisions.

"Healthy population growth numbers not only speak to the city's lure and attraction ... they also play an important role in the allocation of both state and federal revenues," said finance director Mark Vincent. "We need to ensure that the city receives its fair share."

Though the figure is only an estimate, Las Vegas' population is comparable to Boston, Seattle, Washington D.C. and El Paso, Texas.

Since 2002, Las Vegas' population has increased by about 100,000 people, an uptick of almost 20 percent. From 2002 to 2006, the population increased an average of 3.2 percent annually. Population has more than doubled since 1990, when residents numbered about 286,000.

Las Vegas has about a third of Clark County's 1.9 million residents.