Blaine is a city in Whatcom County, Washington, United States. The city's northern boundary is the Canada?US border. Blaine is the shared home of the Peace Arch international monument. The population was 4,684 at the 2010 census. Since Blaine is located right on the border with Canada, it is the northernmost city on Interstate 5, while the southernmost city is San Ysidro, California.