Snohomish County was created out of Island County on January 14, 1861.
As of the census of 2000, there were 606,024 people, 224,852 households, and 157,846 families residing in the county. The population density was 290 people per square mile (112/km²). There were 236,205 housing units at an average density of 113 per square mile (44/km²). The racial makeup of the county was 85.63% White, 1.67% Black or African American, 1.36% Native American, 5.78% Asian, 0.28% Pacific Islander, 1.92% from other races, and 3.36% from two or more races. 4.72% of the population were Hispanic or Latino of any race. 16.2% were of German, 10.0% English, 8.8% Irish, 8.4% Norwegian and 6.6% United States or American ancestry according to Census 2000.
There were 224,852 households out of which 37.30% had children under the age of 18 living with them, 56.00% were married couples living together, 9.80% had a female householder with no husband present, and 29.80% were non-families. 22.60% of all households were made up of individuals and 6.50% had someone living alone who was 65 years of age or older. The average household size was 2.65 and the average family size was 3.13.
In the county, the population was spread out with 27.40% under the age of 18, 8.50% from 18 to 24, 33.00% from 25 to 44, 22.00% from 45 to 64, and 9.10% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 100.10 males. For every 100 females age 18 and over, there were 98.20 males.
The median income for a household in the county was $53,060, and the median income for a family was $60,726. Males had a median income of $43,293 versus $31,386 for females. The per capita income for the county was $23,417. About 4.90% of families and 6.90% of the population were below the poverty line, including 7.60% of those under age 18 and 7.80% of those age 65 or over.
Snohomish County has five major routes that connect the county to the other counties and other areas. There are four north-south routes, which are Interstate 5, Interstate 405, State Route 9, and State Route 99. The only complete east-west route is U.S. Route 2.
Interstates and U.S. Routes
State Routes
Former Routes (PSH/SSH)
Snohomish County is linked by many bus routes from three systems, which are Community Transit, Everett Transit (Everett only), and Sound Transit. The county also has train access from Everett Station for Amtrak's Empire Builder line (to Chicago), and Cascades line (to Vancouver, BC, Edmonds, and Seattle), and Sound Transit's Sounder service to and from Seattle, which links to the South Line that goes to Tacoma.
Community Transit is planning a bus service called SWIFT Bus Rapid Transit from Everett Station to the Aurora Village in Shoreline along the SR 99 corridor. Sound Transit is also planning to extend the Tacoma Link Light Rail service to Seattle and eventually, Everett Station. The line will be known as the North Link.
Snohomish County has one official airport and several municipal airports. The county also is connected by 2 ferry lines operated by Washington State Ferries.
The one official airport is Paine Field, otherwise known as Snohomish County Airport. There are smaller outlying airports, such as Harvey Field in Snohomish. There are 2 municipal airports, Arlington Municipal and Darrington Municipal. There are also two private airports, one in Lake Stevens and another in Granite Falls. The Martha Lake Airport in Martha Lake was a former private airport that was closed in 2000
As said in the introduction above, there are two ferry lines operated by Washington State Ferries in Snohomish County waters that go to and from different counties from the county. The first line is the Edmonds-Kingston line, which carries SR 104. SR 104 terminates in the west at US 101 west of the Kitsap Peninsula, after crossing the Hood Canal over the Hood Canal Bridge. SR 104 terminates in the east at Interstate 5 on the county boundary with King County. The second line is the Mukilteo-Clinton line, which carries SR 525. SR 525 terminates in the west at SR 20 on Whidbey Island, near where SR 20 goes across on another ferry line to US 101. SR 525 terminates in the east at an interchange with Interstate 5, where it continues as Interstate 405.