Birch Bay is a census-designated place (CDP) in Whatcom County, Washington, United States. Birch Bay is a protected bay located between Semiahmoo Bay and Lummi Bay. It is also commonly referred to as the community near and around this body of water, but is actually not its own town. Birch Bay is approximately 100 miles north of Seattle and 35 miles south of Vancouver, BC, Canada. The population was 8,413 at the 2010 census, a 69.6% increase over the 2000 census.
Birch Bay was named in 1792 by Archibald Menzies, a member of the Vancouver Expedition. Vancouver's two ships used Birch Bay as an anchorage for several days. Menzies noted a number of species of birch and gave the name to the bay.