Map - Snohomish County, Washington (Snohomish County)

Snohomish County is a county located in the U.S. state of Washington. With a population of 827,957 as of the 2020 census, it is the third-most populous county in Washington, after nearby King and Pierce counties, and the 75th-most populous in the United States. The county seat and largest city is Everett. The county forms part of the Seattle metropolitan area, which also includes King and Pierce counties to the south.

The county's western portion, facing Puget Sound and other inland waters of the Salish Sea, is home to the majority of its population and major cities. The eastern portion is rugged and includes portions of the Cascade Range, with few settlements along major rivers and most of it designated as part of Mount Baker–Snoqualmie National Forest. Snohomish County is bound to the north by Skagit County, to the east by Chelan County, to the south by King County, and to the west by Kitsap and Island counties.

Snohomish County was created out of Island County on January 14, 1861, and is named for the indigenous Snohomish people. It includes the Tulalip Indian Reservation, which was established by the 1855 Point Elliott Treaty, which relocated several indigenous Coast Salish groups to the reservation. The county seat was originally at the city of Snohomish until an 1897 election moved it to Everett. Since the mid-20th century, areas of Snohomish County have developed into an aerospace manufacturing center, largely due to the presence of Boeing in Everett, as well as bedroom communities for workers in Seattle.

Snohomish County now has 18 incorporated cities and 2 towns with their own local governments, in addition to developed unincorporated areas. It is connected to nearby areas by roads (including Interstate 5), railways, and transit systems. The county government is led by a five-member county council and chief executive elected by voters to four-year terms.

"Snohomish" comes from the name of the largest Native American tribe in the area when settlers arrived in the 19th century. The name is spelled as "Sdoh-doh-hohbsh" in the Lushootseed language and has a disputed meaning with unclear origins. Indian agent Dr. Charles M. Buchanan, who spent 21 years with the Tulalips, once said that he had "never met an Indian who could give a meaning to the word Snohomish". Chief William Shelton, the last hereditary tribal chief of the Snohomish tribe, claimed that it meant "lowland people", a name associated with the tribe's location on the waters of the Puget Sound; other scholars have claimed "a style of union among them", "the braves", or "Sleeping Waters".

The name is also used for the Snohomish River, which runs through part of the county, and the City of Snohomish, the former county seat that was renamed after the formation of the county. The current spelling of the name was adopted by the Surveyor General of Washington Territory in 1857, with earlier documents and accounts using alternative spellings. John Work of the Hudson's Bay Company recorded the name "Sinnahmis" in 1824, while the Wilkes Expedition of 1841 used "Tuxpam" to describe the Snohomish River. The same river was named "Sinahomis" by Captain Henry Kellett in 1847, and was accepted by the U.S. government for several years.