"Plymouth is an unincorporated community in Benton County, Washington, United States. Plymouth is located on the Columbia River across from Umatilla, Oregon. It is south of the Tri-Cities and is served by Interstate 82. It was named by early settlers who felt a nearby rock promontory resembled Plymouth Rock."@en . . . "509" . . "-8" . . . "-7" . . "89.0016"^^ . "Plymouth, Washington"@en . .