- Shelton is a city located in Mason County, Washington, United States. It is situated at the southern end of the Puget Sound region, along the Olympic Peninsula. Shelton is the county seat of Mason County and has a population of around 10,100 people. The city is known for its natural beauty, including the nearby Olympic National Forest and Hood Canal. Shelton is also home to various outdoor recreational activities and hosts the annual Mason County Forest Festival.