Wash. Rev. Code § 36.04.230
Mason county shall consist of the territory bounded as follows, to wit: Commencing in middle of the main channel of Puget Sound where it is intersected in the midchannel of Case's Inlet; thence westerly along the midchannel of Puget Sound, via Dana's Passage, into Totten's Inlet, and up said inlet to its intersection by section line between sections twenty-eight and twenty-nine, township nineteen north, range three west of the Willamette Meridian; thence south to the southwest corner of section thirty-three in township nineteen north, range three west; thence west along the township line dividing townships eighteen and nineteen, twenty miles, to the township line dividing ranges six and seven west, of the Willamette Meridian, which constitutes a part of the east boundary line of Grays Harbor county; thence north along said township line to the sixth standard parallel; thence east along said parallel line to the middle of the channel of Hood Canal; thence southerly along said midchannel to a point due west of the intersection of the shore line of said Hood Canal by the township line between townships twenty-three and twenty-four; thence east along said township line to the line dividing sections three and four in said township twenty-three north, range one west of the Willamette Meridian; thence south along said section line to the head of Case's Inlet; thence south by the midchannel of said inlet to the place of beginning.
RCW 36.04.230