Loon Lake is an unincorporated community and census-designated place in Stevens County, Washington, United States. Loon Lake is located on the northern shore of Loon Lake 5 miles (8.0 km) east of Springdale. The community is served by U.S. Route 395 and Washington State Route 292. Loon Lake has a post office with ZIP code 99148. The community was recognized at the census and had an April 1, 2010 population of 783.