Lynden is a city in Whatcom County, Washington, United States. It is located 15 miles north of Bellingham, the county seat and principal city of the Bellingham Metropolitan Area. It is the second largest city in Whatcom County. The city is approximately 5 miles south of the Canada–U.S. border. The city is located along the Nooksack River and State Route 539. The population of Lynden was 15,749 at the 2020 census. The city is also home to the annual Northwest Washington Fair.