Belfair is an unincorporated community 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. The population of the surrounding area swells in the summertime as tourists and nature lovers flock to the Canal and the Olympic Peninsula. The population within the Urban Growth Area (UGA) is an estimated 700.
Belfair 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.