Idaho Code § 31-132
Lemhi county is described as follows: beginning at a point where the divide between the watersheds of the Salmon river and the Clearwater river in the state of Idaho intersect the boundary line between the state of Idaho and the state of Montana; thence in a southwesterly direction along said divide to its junction with the divide between the watershed of Horse creek on the east and watershed of Squaw creek and other creeks on the west; thence southerly along said divide between Horse creek on the east, and Squaw creek and other creeks on the west, to Salmon river; thence along the center line of the middle of the stream of Salmon river southeasterly and up stream to the confluence of the Middle Fork of Salmon river with the main Salmon river in the state of Idaho; thence southerly along the center line of the middle of the channel of the said Middle Fork of the Salmon river to the mouth of Loon creek (1903, p. 48); thence up Loon creek to the mouth of Warm Spring creek; thence up Warm Spring creek to the divide which separates the waters of Yankee Fork on the south and Loon and Deep creeks on the north, and following the said divide in an easterly direction around the head of Panther creek to the divide between Hat creek and Ellis creek; thence on the divide between Hat and Ellis creeks in an easterly direction to the Salmon river; thence up the main channel of said Salmon river to the confluence of the Pahsimeroi river with the Salmon river; thence up the Pahsimeroi river to the mouth of Big creek; thence up Big creek and on a line from the head thereof with a general course of the said creek to the summit of the divide between the waters of the Pahsimeroi river and the Lemhi river; thence southeasterly on the summit of the said divide to a point west from the headwaters of the Little Lost river; thence east to the headwaters of the Little Lost river; thence down the Little Lost river (15 Ter. Sess. 26) to the intersection of the same with the township line between townships ten (10) and eleven (11) north; thence east along the said township line (1899, p. 111), to the southwest corner of township eleven (11) north, range thirty-one (31) east; thence north along the range line between ranges thirty (30) and thirty-one (31) east, to the intersection of the same with the boundary line of the state of Montana (1899, p. 273); thence generally in a northwesterly direction along the said state boundary line to the point of beginning.
County seat-Salmon.
Idaho Code § 31-132