list of counties in Washington

The U.S. state of Washington has 39 counties. The Provisional Government of Oregon established Vancouver and Lewis Counties in 1845 in unorganized Oregon Country, extending from the Columbia River north to 54°40′ north latitude. After the region was organized within the Oregon Territory with the current northern border of 49° north, Vancouver County was renamed Clark, and six more counties were created out of Lewis County before the organization of Washington Territory in 1853; 28 were formed during Washington's territorial period, two of which only existed briefly. The final five were established in the 22 years after Washington was admitted to the Union as the 42nd state in 1889.

Article XI of the Washington State Constitution addresses the organization of counties. New counties must have a population of at least 2,000 and no county can be reduced to a population below 4,000 due to partitioning to create a new county. To alter the area of a county, the state constitution requires a petition of the "majority of the voters" in that area. A number of county partition proposals in the 1990s interpreted this as a majority of people who voted, until a 1998 ruling by the Washington Supreme Court clarified that they would need a majority of registered voters. No changes to counties have been made since the formation of Pend Oreille County in 1911, except when the small area of Cliffdell was moved from Kittitas to Yakima County in 1970.