Sumas (soo-MAS) is a city in Whatcom County, Washington, United States. It had a population of 1,307 as of the 2010 census. Take a look below for 10 fun and amazing facts about Sumas, Washington, United States. 1. Sumas is located adjacent to the Canada–U.S. border and borders the city of Abbotsford, British Columbia. 2….