Whatcom County (/ˈwɒtkəm/, /ˈhwɒtkəm/) is a county located in the northwestern corner of the U.S. state of Washington, bordered by the Lower Mainland (the Metro Vancouver and Fraser Valley Regional Districts) of the Canadian province of British Columbia to the north, Okanogan County to the east, Skagit County to the south, San Juan County across Rosario Strait to the southwest, and the Strait of Georgia to the west. Its county seat and largest population center is the coastal city of Bellingham. Whatcom County is coterminous with the Bellingham, WA Metropolitan Statistical Area. As of the 2020 census, the county's population was 226,847.
The county was created from Island County by the Washington Territorial Legislature in March 1854. It originally included the territory of present-day San Juan and Skagit counties, which were later independently organized after additional settlement. Its name derives from the Lummi word Xwotʼqom, also spelled [x̣ʷátqʷəm], perhaps meaning 'noisy' or 'noisy water' and referring to a waterfall. Whatcom County has a diversified economy with a significant agricultural base, including approximately 60% of the nation's annual production of raspberries.