Whatcom County is a county located in the U.S. state of Washington. As of the 2010 census, the population was 201,140. The county seat and largest city is Bellingham. The county was created out of Island County by the Washington Territorial Legislature on March 9, 1854, and originally included present day San Juan and Skagit Counties. Its name ultimately derives from the Lummi word Xwot'qom, meaning "noisy water."