Arlington is a city in northern Snohomish County, Washington, United States, part of the Seattle metropolitan area. The city lies on the Stillaguamish River in the western foothills of the Cascade Range, adjacent to the city of Marysville. It is approximately 10 miles north of Everett, the county seat, and 40 miles north of Seattle, the region's largest city. As of the 2010 U.S. census, Arlington has a population of 17,926.
Arlington was established in the 1880s by settlers and the area was platted as two towns, Arlington and Haller City. Haller City was absorbed by the larger Arlington, which was incorporated as a city in 1903. During the Great Depression of the 1930s, the Arlington area was the site of major projects undertaken for employment under the direction of federal relief agencies, including construction of a municipal airport that would serve as a naval air station during World War II. Beginning in the 1980s, Arlington was affected by suburbanization due to the expansion of Seattle, growing by more than 450 percent by 2000 and annexing the unincorporated area of Smokey Point to the southwest.