Idaho Code § 31-110
Boise county is described as follows: beginning at the confluence of Mores creek with the Boise river, at the center of the channel of Boise river;
Western boundary. Thence north forty-four (44) degrees and thirty-eight (38) minutes west (R.C., section 23f), until the said line intersects the north line of township five (5) north; thence east along the north boundary of township five (5) north to the northeast corner of township five (5) north, range one (1) east; thence north twenty-four (24) miles to the northeast corner of township nine (9) north, range one (1) east;
Northern boundary. Thence east (1915, ch. 165, section 2, p. 363) along the second (2) standard parallel north, to the center of the North Fork of the Payette river; thence northerly along the river to the intersection with the line between townships ten (10) and eleven (11) north; thence east to the ridge dividing the waters of the Salmon and Payette rivers (1917, ch. 99, section 2, p. 361); thence in an easterly direction along the divide which separates the waters of the Payette river and its tributaries from the waters of Salmon river and its tributaries (Special and Local Laws, 120), to the head of the Middle Fork of Salmon river;
Eastern boundary. Thence southerly along the divide which separates the water flowing into the South Payette river and Bear Valley creek from that flowing into the main Salmon river and Cape Horn creek to the summit of the Sawtooth mountains; thence southerly along the summit of the Sawtooth mountains (15 Ter. Ses. 26) to the headwaters of the North Fork of Boise river;
Southern boundary. Thence down the center of the channel of the North Fork of Boise river and the main Boise river to the place of beginning (3 Ter. Ses. 214).
County seat-Idaho City.
Idaho Code § 31-110