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 became home to projects under the direction of federal relief agencies, including a municipal airport that would serve as a naval air station during World War II.