Wash. Rev. Code § 36.04.220
Lincoln county shall consist of the territory bounded as follows, to wit: Beginning at the point in township twenty-seven north, where the Colville Guide Meridian between ranges thirty-nine and forty east, Willamette Meridian, intersects the Spokane river, and running thence south along said meridian line to the township line between townships twenty and twenty-one north; thence west along said township line to its intersection with the Columbia Guide Meridian between ranges thirty and thirty-one east, Willamette Meridian; thence north along said meridian line to a point where it intersects the midchannel of the Columbia river; thence up said river in the middle of the channel thereof to the mouth of the Spokane river; thence up the Spokane river, in the middle of the channel thereof, to the place of beginning.
RCW 36.04.220