Wash. Rev. Code § 36.04.250
Pacific county shall consist of the territory bounded as follows, to wit: Commencing at the midchannel of the Columbia river at the point of intersection of the line between ranges eight and nine west; thence north along said line to the north boundary of township ten north; thence east along said boundary to the line between ranges five and six west; thence north along the west boundary of range five west to the northwest corner of section eighteen in township fifteen north, range five west; thence west to the west boundary of the state in the Pacific Ocean; thence southerly along said boundary, including Shoalwater Bay, to a point opposite Cape Disappointment; thence up midchannel of the Columbia river to the place of beginning.
RCW 36.04.250