PASCO -- Tri-Citians have only to look at all the homes that have sprung up in west Pasco to know the city has boomed to become the second largest of the Tri-Cities.

Turns out all that growth also made Franklin County the 18th-fastest growing county in the nation between 2000 and 2009, according to new U.S. Census Bureau figures. No other Washington county made the census' top 100 list.

Census figures indicate Franklin County's population was about 77,355 in July 2009 -- up 56.8 percent since 2000, when it had 49,602 residents.

Benton County's population was estimated at 168,294 in 2009. That was up 17.5 percent from the 143,108 people counted in the 2000 Census.

Before 2000, there wasn't much more than some soccer fields around Road 68 north of Interstate 182, said Rick White, Pasco community and economic development director.

Then the housing market boomed from 2003-06, with the city issuing about 1,000 building permits for single-family homes each year, he said.

That fast rate of residential growth meant the city got some immediate economic benefits from sales tax and state-shared revenues, White said. But that growth came with added service costs as well, which meant adding police and fire personnel and general city staff.

So far in 2010, the city has issued 170 permits for single-family homes, White said. If that trend continues, the city could have 750 new homes this year.

Growth over the past decade has also increased the number of students attending Pasco schools. Since 2000, the district has gained 5,600 students, enough to fill nine elementary schools.

Because of the growth, the district added schools. Chiawana High School, Pasco's second high school, was opened this year.

That allowed the district to turn the annex at Pasco High into an elementary school called Captain Gray Early Learning Center. The district has also added Virgie Robinson and Maya Angelou elementary schools and Ellen Ochoa Middle School since 2000.

Pasco's population had been underestimated by about 3,000 people before the 2000 Census corrected the number. White said he wouldn't be surprised if the 2010 Census, which was sent out last week, results in a similar correction.

Getting a correct population count is important, said Marie Mosley, Kennewick's director of support services.

"We receive state-shared revenues based on population," she explained. "That is how the money for criminal justice, fuel taxes and liquor excise taxes are distributed."

The Municipal Research and Services Center of Washington estimates the per capita distribution of those revenue sources will be $36.68 this year.

For Kennewick, which has a population of about 68,000, that would be $2.5 million. Pasco's estimated 56,000 residents would mean about $2 million. Richland's estimate for 2010 was not available, but with its 2009 estimated population of 48,000, it would get about $1.8 million.

The Census Bureau will release national and state statistics from the 2010 Census in December. County and city information will be released in April 2011.

Washington is expected to gain a U.S. representative after new population figures are released, bringing the state to 10 representatives in Congress.

-- Staff reporters John Trumbo and Sara Schilling contributed to this report.

-- Kristi Pihl: 582-1512; kpihl@tricityherald.com