Cathcart, Washington (Wikipedia)Cathcart is a census-designated place (CDP) in Snohomish County, Washington, United States. The population was 2,458 at the 2010 census. Based on per capita income, one of the more reliable measures of affluence, Cathcart ranks 45th of 522 areas in the state of Washington to be ranked. Cathcart was named for Isaac Cathcart, a lumberman, entrepreneur, and Snohomish County pioneer.