Idaho Code § 31-133
Lewis county is described as follows: beginning at the mouth of Lolo creek;
Northern boundary. Thence in a northerly direction down the middle of the channel of the Clearwater river to a point where the seventh (7th) standard parallel north crosses the Clearwater river; thence west along said parallel to a point where the same intersects Little Canyon creek; thence down the center of the channel of Little Canyon creek to a point where the same empties into Big Canyon creek; thence up the center of the channel of the Big Canyon creek to a point where the same crosses the township line between townships thirty-four (34) and thirty-five (35) north; thence west on said township line, to a point where the same crosses Mission creek;
Western boundary. Thence up the middle of the channel of Mission creek to a point where the same crosses the township line between townships thirty-three (33) and thirty-four (34) north; thence west on said township line to the northeast corner of section four (4), township thirty-three (33) north, range three (3) west; thence south on section lines to the center of the channel of Salmon river;
Southern boundary. Thence up the center of the channel of Salmon river to the mouth of Deep creek; thence up the middle of the channel of Deep creek to the mouth of the Right Fork of Deep creek; thence up the middle of the channel of the Right Fork of Deep creek to a point where the line between ranges one (1) and two (2) west, crosses said Deep creek; thence north along said line to the point where the said line crosses Willow creek; thence down the middle of the channel of Willow creek to its junction with Lawyer's canyon; thence down the middle of the channel of Lawyer's canyon to its junction with the Clearwater river;
Eastern boundary. Thence down the middle of the channel of Clearwater river to the mouth of Lolo creek, the place of beginning.
County seat-Nez Perce.
Idaho Code § 31-133