Chain Lake is a census-designated place (CDP) in Snohomish County, Washington, United States. The population was 3,741 at the 2010 census.GeographyChain Lake is located at .According to the United States Census Bureau, the CDP has a total area of 10.60 square miles, of which, 10.55 square miles of it is land and 0.05 square miles of it is water.