Blaine is a city in Whatcom County, Washington, United States. The city's northern boundary is the Canada–U.S. border; the Peace Arch international monument straddles the border of both countries. It is the fourth largest incorporated city within the Bellingham Metropolitan Area. The population was 5,884 at the 2020 census. As Blaine is located adjacent to the border with Canada, it is the northernmost city on Interstate 5.