Idaho Code § 31-112
Bonneville county is described as follows: beginning at the northeast corner of Bannock county;
Southern boundary. Thence west along the north line of Bannock county to the southwest corner of township four (4) south, range forty-two (42) east; thence north along the range line between ranges forty-one (41) and forty-two (42) east, to the southeast corner of township one (1) south, range forty-one (41) east; thence west along the township line between township one (1) and township two (2) south, to the southwest corner of township one (1) south, range forty (40) east; thence north along the range line to the base line; thence west along the base line to the southwest corner of township one (1) north, range thirty-eight (38) east; thence north along the range line to the northeast corner of section twenty-four (24), township one (1) north, range thirty-seven (37) east; thence west along section lines to the southwest corner of section fifteen (15), township one (1) north, range thirty-seven (37) east; thence north along the section line to the northwest corner of said section fifteen (15), township one (1) north, range thirty-seven (37) east; thence west, following the section lines to the range line between ranges thirty-three (33) and thirty-four (34) east;
Western boundary. Thence north (1911, ch. 5, section 2, pp. 8, 9) to the line between townships three (3) and four (4) north;
Northern boundary. Thence east along the said township line between townships three (3) and four (4) north (1893, p. 94), to a point where the said line bisects the top or comb of the Big Hole mountain range; thence following along the top or comb of the said mountains in a southeasterly direction (R.C., section 23l) to the west line of the state of Wyoming;
Eastern boundary. Thence south along the west line of the state of Wyoming to the point of beginning (1911, ch. 5, section 2, p. 9).
County seat-Idaho Falls.
Idaho Code § 31-112