Mountlake Terrace is a suburban city in Snohomish County, Washington, United States. It lies on the southern border of the county, adjacent to Shoreline and Lynnwood, and is 13 miles north of Seattle. The city had a population of 19,909 people counted in the 2010 census. Mountlake Terrace was founded in 1949 by real estate developers on the site of a disused airfield, intending to provide low-cost housing for veterans.