Idaho Code § 31-146
Washington county is described as follows: beginning at a point on the boundary line between the states of Idaho and Oregon, the same being the middle of the center channel of Snake river, three thousand nine hundred sixty (3,960) feet in a southwesterly direction from the mouth of Wildhorse river;
Northern boundary. Thence in an easterly direction fifteen and one-half (15 1/2) miles, to a point one-half (1/2) mile east of the west quarter (W1/4) corner of section six (6), township seventeen (17) north, range two (2) west; thence south about twelve (12) miles, to the intersection of said line with Cow creek; thence southeast down the center line of Cow creek to its confluence with the Weiser river; thence south across the Weiser river to a point five hundred (500) feet east of the north quarter (N1/4) corner of section twenty-nine (29), township fifteen (15) north, range two (2) west; thence east about three and three-quarters (3 3/4) miles, to a point one thousand three hundred twenty (1,320) feet east of the northwest corner of section twenty-five (25), said township and range; thence south eight and one-half (8 1/2) miles, to a point one thousand three hundred twenty (1,320) feet east of the west quarter (W1/4) corner of section one (1), township thirteen (13) north, range two (2) west; thence in a southeasterly direction six and one-half (6 1/2) miles, to a point one thousand three hundred twenty (1,320) feet south and one thousand three hundred twenty (1,320) feet east of the west quarter (W1/4) corner of section twenty-four (24), township thirteen (13) north, range one (1) west; thence east (1911, ch. 31, section 2, p. 67) to the summit of the dividing range between the waters of Crane creek on the west and Squaw creek on the east;
Eastern boundary. Thence southerly along the summit of said dividing range to the intersection of said dividing ridge with the second (2d) standard parallel north (R.C., section 23f);
Southern boundary. Thence west along said second (2d) standard parallel to its intersection with the Snake river;
Western boundary. Thence down the main channel of Snake river, to the place of beginning (R.C., section 23w).
County seat-Weiser.
Idaho Code § 31-146