Sheriff's Department vehicle in Bellingham. Whatcom County /ˈhwɒtkəm/ is a county located in the U.S. state of Washington. As of the 2010 census, the population was 201,140. It is bordered by Canada on the north, Okanogan County on the east, Skagit County on the south, and the Strait of Georgia on the west. The county seat and largest city is Bellingham.