sr 107 begins at an intersection with us 101 in rural grays harbor county between cosmopolis and raymond. the highway travels north along the little north river and east along the chehalis river through the communities of preachers slough and melbourne. sr 107 turns north in south montesano and crosses the chehalis river into the city of montesano before the designation ends at a diamond interchange with us 12, while the roadway continues north as main street into the city.