Allyn is a census-designated place (CDP) in Mason County, Washington, United States.

Allyn is located on the western shore of the North Bay region of the Case Inlet of Puget Sound.

[2] By 1890 Allyn had a post office, school, newspaper, sawmill, two saloons, a hotel and wharf.

[4] From the 1870s to the 1920s, transportation needs for Allyn and other communities along Case Inlet were once served by a small flotilla of steamboats.

[5] The local community based monthly newspaper, called the North Bay Review, services Allyn.