Belfair is a census-designated place in Mason County, Washington, United States.Located on the Union River, headwaters of the Hood Canal, a branch of Puget Sound, it serves as the commercial center of North Mason County.elfair is located on an isthmus connecting the Kitsap and Olympic Peninsula. It receives an average rainfall of 60 inches (1,500 mm) yearly and has a growing season of 212 days. Mason Lake is 8 miles (13 km) southwest of Belfair. Belfair is the home of U.S. Representative Norm Dicks.