Idaho Code § 31-127
Idaho county is described as follows: beginning at the junction of the Salmon river with the Snake river;
Northern boundary. Thence up the middle 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 Deep creek; thence north along the 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; thence down the middle of the channel of Clearwater river to the mouth of Lolo creek; thence up the middle of the channel of Lolo creek to the head of Lolo creek; thence in a direct line to the Lolo pass at the summit of the Bitter Root mountains;
Eastern boundary. Thence southeasterly and southerly following the present defined boundary line between the state of Idaho and the state of Montana (1899, p. 79), to a point directly north of the confluence of the Middle Fork of Salmon river with the main Salmon river in the state of Idaho; thence south to the confluence of the Middle Fork of Salmon river with the main Salmon river; thence southerly along the center line or middle of the channel of said Middle Fork of Salmon river (R.C., section 23m), to its intersection with the fifth (5th) standard parallel north;
Southern boundary. Thence west along said parallel to the divide separating the waters of the Salmon and Payette rivers; thence westerly and southerly (1917, ch. 99, section 2, p. 360), along said divide, to the line of Adams county, at a point east of the northern point of Little Salmon Meadows; thence west to the Little Salmon river; thence down the Little Salmon river to a point east of the point where the section line between sections six (6) and seven (7), township twenty-two (22) north, range one (1) east, intersects the said meridian; thence west to the middle of the main channel of Snake river.
Western boundary. Thence down the middle of the main channel of Snake river, to the mouth of Salmon river, the place of beginning (R.C., section 23m).
County seat-Grangeville.
Idaho Code § 31-127