Fueled by its biggest growth spurt so far this decade, Thurston County edged past Yakima County to become the state's seventh most populous county, according to federal estimates released Thursday.
The U.S. Census Bureau said the estimated population of Thurston County increased 5,789 people to 234,670 for the year ending July 1, 2006. Yakima County's population was 233,105, growing just under 1 percent.
Thurston County's population grew 2.5 percent. The increases had ranged between 1.6 and 2 percent annually since July 2000.
Thurston isn't far from becoming the sixth-largest county. Kitsap County lost more than 900 people in the last year and now has a population of 240,604.
The Pasco area was the fastest-growing part of Washington in the past year, with Franklin County growing an estimated 5.7 percent in 2006 from the year before.
Franklin County added an estimated 3,598 people during the year, growing to 66,570 residents, the bureau said.
The county has a strong farm economy and is also near the Hanford nuclear reservation and its many jobs.
Statewide, Washington grew 1.7 percent, adding 103,899 residents for a total of 6,395,789, making it the second-most-populous state in the West after California.
King County, which includes Seattle, remained by far the largest county in the state, growing 1.5 percent over the year to 1,826,732 residents. King also added the greatest number of residents, 27,613.
The rest of the top 10 counties by population in the state remained in the same order, except for Thurston and Yakima counties, which switched places.
The only counties in Washington to lose population were Garfield, home of Pomeroy and the state's smallest county, down 3.1 percent to 2,223 people; Columbia, home of Dayton, down 1.3 percent to 4,087 residents; Whitman, home of Pullman, down 0.7 percent to 39,838 people; and Kitsap, home of Bremerton, down 0.4 percent to 240,604 people.
Other big gainers by percentage were Wahkiakum County, up 3.6 percent to 4,026; Mason County, up 3.3 percent to 55,951 and Cowlitz County, up 2.8 percent to 99,905 people.
Washington has had steady growth since the 2000 census, when the state had 5.9 million residents.
For King County, the population trend represents a change from recent years. In 2006, more people moved to King County from elsewhere than left for another county, reversing a trend going back at least to 2000.
"It absolutely has everything to do with the fact that we continued to lose jobs, especially in the Seattle area, straight through to 2004," King County regional labor economist Cristina Gonzalez said.
The Census Bureau estimates annual county population totals as of July 1, using local records of births and deaths, Internal Revenue Service records of people moving within the United States and statistics on immigrants.
Among the bureau's findings nationally:
* Of the five U.S. counties that lost the most people from 2005 to 2006, four were hit by Hurricane Katrina. The biggest decrease was in Orleans Parish, where the population dropped by nearly 229,000, to about 223,400.
* Maricopa County, Ariz., home to Phoenix, added the most people from 2005 to 2006: nearly 130,000, to about 3.8 million.* Chattahoochee County, Ga., had the highest percentage growth from 2005 to 2006, at 13.2 percent, to just over 14,000 people.
The top 10 counties in population estimates as of July 1, 2006, according to the U.S. Census Bureau, were:
King: 1.8 million, up 27,613 residents
Pierce: 766,878, up 13,669
Snohomish: 669,887, up 14,323
Spokane: 446,706, up 6,272
Clark: 412,938, up 8,872
Kitsap: 240,604, down 921
Thurston: 234,670, up 5,789
Yakima: 233,105, up 2,168
Whatcom: 185,953, up 2,590
Benton: 159,463, up 1,543
Christian Hill of The Olympian contributed to this report.