# List of state highways in Idaho

The Idaho Transportation Department (ITD) is responsible for the establishment and classification of a state highway network, including 5,000 miles (8,000 km) of roads that are classified as Interstate Highways, U.S. Highways, and state highways within the state of Idaho in the United States. The current state highway marker consists of a white background, black numbering, and a solid black geographic outline of the state of Idaho.

## History

During the 1920s, in lieu of numbering its highways, Idaho had a system of lettered Sampson Trails. They were marked by businessman Charles B. Sampson of Boise at no expense to the state, using orange-colored shields. By 1929, the trails system had included 6,500 miles (10,500 km) of marked highways that covered most of the state. By the mid-1930s, the state had adopted a more standard system of numbered state highways.
In 1978, the ITD began using brown state highway markers to denote scenic Idaho highways, in addition to the main highway markers that featured a black background and white lettering and the name "IDAHO" in black lettering inside a white geographic outline of the state. The brown markers were discontinued around 2012, and in April 2020, ITD changed the coloring of the main state highway marker to its current color scheme, also adding a wide version of the marker for three-digit highways and removing the word "IDAHO" from all markers in the process.

## Sampson Trails

The following Sampson Trails were marked:
* A, Boise to Wyoming via Twin Falls and Pocatello; became US-30 and US-30N
* B, Boise to Canada via Lewiston and Coeur d'Alene; became US-30, US-30N, US-95, and SH-1
* C, Pocatello to Montana via Idaho Falls; became US-91 and US-191
* D, Boise to New Meadows via Banks; became SH-15 (today's SH-55)
* E, not on the 1926 map
* F, Boise to Blackfoot via Stanley; became SH-21, SH-17, US-93 (today's SH-75), and SH-27
* G, Mountain Home to Picabo via Fairfield; became SH-22 (today's US-20)
* H, Bliss to Trude via Arco; became SH-24, SH-23, SH-22, SH-29, and an unnumbered road (today's US-20 and US-26)
* I, Pioneer to Idaho Falls; became an unnumbered road
* J, Nevada to Shoshone via Twin Falls; became US-93
* K, Utah to McCammon via Preston; became US-91
* L, not on the 1926 map
* M, Washington to Montana via Coeur d'Alene; became US-10
* N, Bonners Ferry to Montana; became US-2
* O, Oregon to Caldwell; became SH-49 and SH-18
* P, Utah to Downey; became SH-36
* Q, Declo to Fairfield; became SH-25 and SH-46
* R, not on the 1926 map
* S, Oregon to Nampa; became unnumbered road and SH-45
* T, Star to Grimes Pass; became SH-16, unnumbered road, and SH-17
* U, Utah to Montpelier; became SH-35
* V, Hailey to Stanley; became US-93 (today's SH-75)
* W, not on the 1926 map
* X, not on the 1926 map
* Y, Bonners Ferry to Canada; became US-95

## State highways

| Number | Length (mi) | Length (km) | Southern or western terminus | Northern or eastern terminus | Formed | Removed | Notes |
| SH-1 | 12.279 | 19.761 | US-95 near Copeland | Hwy 21 at Porthill | 01932-01-011932 | current | |
| SH-3 | — | — | US-95 / US-195 (now US 2) in Ponderay | MT 3 near Clark Fork | 01929-01-011929 | 01940-01-011940 | Replaced by US-10 Alternate |
| SH-3 | 117.680 | 189.388 | US-12 near Spalding | I-90 near Rose Lake | 01953-01-011953 | current | |
| SH-4 | 7.380 | 11.877 | I-90 in Wallace | National Forest Road No. 7623 at Burke | 01929-01-011929 | current | |
| SH-5 | 19.140 | 30.803 | US-95 in Plummer | SH-3 in Saint Maries | 01929-01-011929 | current | |
| SH-6 | 40.645 | 65.412 | SR 272 near Potlatch | SH-3 near Santa | 01929-01-011929 | current | |
| SH-7 | 16.563 | 26.656 | Russell Ridge Road near Orofino | Old Highway 7 in Ahsahka | 01929-01-011929 | current | Formerly continued north to Harvard and south to Grangeville |
| SH-8 | 53.589 | 86.243 | SR 270 in Moscow | 1st Street in Elk River | 01929-01-011929 | current | |
| SH-9 | — | — | US-95 in Spalding | S-412 at the Montana state line | 01929-01-011929 | 01962-01-011962 | Replaced by US-12 |
| SH-9 | 13.522 | 21.762 | SH-8 near Deary | SH-6 near Harvard | 01965-01-011965 | current | |
| SH-10 | — | — | SH-7 in Greencreek | SH-9 (now US 12) in Kamiah | 01952-01-011952 | 01953-01-011953 | Duplicated US 10; renumbered SH-62 |
| SH-11 | 42.481 | 68.367 | US-12 in Greer | Forest Service Road No. 247 near Headquarters | 01929-01-011929 | current | |
| SH-12 | — | — | US-95 Business in Craigmont | SH-62 in Kamiah | 01929-01-011929 | 01962-01-011962 | Renumbered SH-64 because US-12 extended into Idaho |
| SH-13 | 26.390 | 42.471 | US-95 in Grangeville | US-12 near Kooskia | 01929-01-011929 | current | |
| SH-14 | 49.515 | 79.687 | SH-13 near Harpster | Airport Road in Elk City | 01929-01-011929 | current | |
| SH-15 | — | — | US-95 near Marsing | US-30 in Boise | 01929-01-011929 | 01967-01-011967 | Renumbered as SH-55 (which continued west from Boise) because of I-15 |
| SH-16 | 16.005 | 25.758 | US-26 near Star | SH-52 in Emmett | 01929-01-011929 | current | |
| SH-17 | — | — | SH-15 (now SH-55) in Banks | Crouch | 01929-01-011929 | 01960-01-011960 | Now Banks-Lowman road; formerly continued east to Lowman; until 1938 continued east to Stanley; |
| SH-18 | — | — | US-30 in Fruitland | US-30 in Caldwell | 01929-01-011929 | 01940-01-011940 | Replaced by US-95 and US-20 (US-26 was added to this section of US-20 as a concurrency in 1952) |
| SH-18 | — | — | Oregon state line | US-95 in Parma | 01953-01-011953 | 01975-01-011975 | Now Wanstad Road and Roswell Road |
| SH-19 | 19.915 | 32.050 | OR 201 near Homedale | I-84 Business in Caldwell | 01929-01-011929 | current | |
| SH-20 | — | — | US-95 near Marsing | US-30 near Nampa | 01929-01-011929 | 01953-01-011953 | Renumbered SH-72 because US-20 extended into Idaho; now part of SH-55; until 1939, continued southwest to Oregon state line |
| SH-21 | 130.869 | 210.613 | I-84 in Boise | SH-75 in Stanley | 01929-01-011929 | current | |
| SH-22 | 43.936 | 70.708 | SH-33 near Howe | I-15 in Dubois | 01929-01-011929 | current | Originally continued west to Mountain Home |
| SH-23 | — | — | US-93 in Shoshone | SH-22 in Carey | 01929-01-011929 | 01941-01-011941 | Replaced by US-93 Alternate (now US-93) and US-20 Temp (now US-26) |
| SH-23 | — | — | US-93 (now SH-75) in Bellevue | SH-68 (now US-20) in Picabo | 01953-01-011953 | 01971-01-011971 | Now Gannett Road; originally continued east to Carey |
| SH-24 | 67.533 | 108.684 | I-84 / US-30 in Heyburn | US-93 in Shoshone | 01929-01-011929 | current | Originally continued west to Bliss |
| SH-25 | 58.048 | 93.419 | I-84 near Jerome | I-84 / SH-77 near Declo | 01929-01-011929 | current | |
| SH-26 | 7.835 | 12.609 | US-93 near Knull | US-30 in Twin Falls | 01929-01-011929 | 01953-01-011953 | Renumbered SH-74 because US-26 extended into Idaho |
| SH-27 | 7.835 | 12.609 | US-93 in Challis | US-91 in Blackfoot | 01929-01-011929 | 01941-01-011941 | Replaced by US-93 Alternate (now US-93) and US-20 (now US-26) |
| SH-27 | 26.561 | 42.746 | Main Street in Oakley | SH-25 in Paul | 01950-01-011950 | current | |
| SH-28 | 135.645 | 218.299 | SH-33 near Mud Lake | US-93 in Salmon | 01929-01-011929 | current | |
| SH-29 | — | — | SH-27 (now US-26) in Arco | US-91 in Dubois | 01929-01-011929 | 01938-01-011938 | Replaced by SH-22 |
| SH-29 | — | — | US-91 in Idaho Falls | Wyoming border | 01938-01-011938 | 01952-01-011952 | Former portion of SH-22; replaced by US-26 |
| SH-29 | 13.614 | 21.910 | SH-28 in Leadore | Montana Secondary Highway 324 at Bannock Pass | 01953-01-011953 | current | |
| SH-31 | — | — | US-191 (now US 20) in Island Park | Montana state line at Raynolds Pass | 01929-01-011929 | 01934-01-011934 | Later restored as SH-96, later SH-287, now later SH-87 |
| SH-31 | 21.025 | 33.836 | US-26 in Swan Valley | SH-33 in Victor | 01934-01-011934 | current | |
| SH-32 | 28.386 | 45.683 | SH-33 near Tetonia | SH-47 near Ashton | 01929-01-011929 | current | |
| SH-33 | 155.084 | 249.584 | US-20 / US-26 near Arco | WYO 22 near Victor | 01929-01-011929 | current | |
| SH-34 | 105.980 | 170.558 | US-91 / SH-36 in Preston | WYO 239 near Freedom | 01929-01-011929 | current | Formerly continued south to the Utah border |
| SH-35 | — | — | SH-40 (now US-89) in Geneva | Utah state line | 01929-01-011929 | 01939-01-011939 | Replaced by US-89 |
| SH-35 | — | — | US-91 in Red Rock Junction | Utah state line | 01953-01-011953 | 01962-01-011962 | Now Old Oxford Highway and Oxford Highway |
| SH-36 | — | — | US-91 in Downey | Utah state line | 01929-01-011929 | 01938-01-011938 | replaced by US-191 (now I-15) |
| SH-36 | 73.313 | 117.986 | I-15 near Malad City | US-89 in Ovid | 01962-01-011962 | current | |
| SH-37 | 31.231 | 50.261 | Onedia–Power county line near Holbrook | I-86 near American Falls | 01929-01-011929 | current | Formerly continued to Malad City |
| SH-38 | — | — | Power/Bannock County Line south of Pocatello | SH-37 east of Holbrook | 01929-01-011929 | 01960-01-011960 | Now Arbon Valley Road, Arbon Valley Highway, and Bannock Highway; continued north to Pocatello until 1955 |
| SH-38 | 23.438 | 37.720 | North Holbrook Road near Holbrook | I-15 in Malad City | 01985-01-011985 | current | Formerly part of SH-37 |
| SH-39 | 52.924 | 85.173 | I-86 in American Falls | US-26 in Blackfoot | 01929-01-011929 | current | |
| SH-40 | — | — | Wyoming state line | SH-35 (now US-89) in Geneva | 01929-01-011929 | 01939-01-011939 | Replaced by US-89 |
| SH-40 | 2.737 | 4.405 | I-15 near Downey | US-91 in Downey | 01972-01-011972 | current | |
| SH-41 | 39.058 | 62.858 | I-90 in Post Falls | US-2 in Oldtown | 01931-01-011931 | current | |
| SH-42 | — | — | SH-7 in Kendrick | US-12 near Spalding | 01934-01-011934 | 01965-01-011965 | Replaced by SH-3; originally continued north to Harvard |
| SH-43 | — | — | SH-7 in Ahsahka | SH-42 in Kendrick | 01934-01-011934 | 01946-01-011946 | Restored as part of rerouted SH-7 in 1953; now Old Highway 7 |
| SH-43 | — | — | US-95 Alternate near Santa | Elk River | 01953-01-011953 | 01965-01-011965 | Replaced by SH-3 and SH-8 |
| SH-43 | 3.868 | 6.225 | US-26 at Beachs Corner | US-20 in Ucon | 01978-01-011978 | current | |
| SH-44 | 23.089 | 37.158 | I-84 near Caldwell | US-20 / US-26 in Garden City | 01934-01-011934 | current | |
| SH-45 | 17.985 | 28.944 | SH-78 at Walters Ferry | I-84 Business in Nampa | 01934-01-011934 | current | |
| SH-46 | 43.052 | 69.285 | I-84 near Wendell | US-20 near Fairfield | 01935-01-011935 | current | |
| SH-47 | 12.420 | 19.988 | US-20 near Warm River | Wyoming state line | 01935-01-011935 | 01957-01-011957 | |
| SH-47 | 12.420 | 19.988 | US-20 in Ashton | Caribou-Targhee National Forest near Warm River | 01958-01-011958 | current | |
| SH-48 | 24.409 | 39.282 | I-15 near Roberts | US-26 Business in Ririe | 01935-01-011935 | current | |
| SH-49 | — | — | Washington state line | US-95 near Parma | 01937-01-011937 | 01940-01-011940 | Replaced by US-20 (US-26 was added to this section of US-20 as a concurrency in 1952) |
| SH-49 | — | — | SH-48 near Menan | 97th north near Idaho Falls | 01953-01-011953 | 01962-01-011962 | Until 1957, continued south to US 20/US 191 (now Business US 20); now 5th East/3400 East, 100 North, and 3500 East |
| SH-50 | 8.092 | 13.023 | US-30 near Kimberly | SH-25 near Eden | 01938-01-011938 | current | |
| SH-51 | 93.598 | 150.631 | Nevada State Route 225 near Owyhee, Nevada | I-84 Business in Mountain Home | 01938-01-011938 | current | |
| SH-52 | 54.126 | 87.107 | OR 52 in Payette | SH-55 in Horseshoe Bend | 01938-01-011938 | current | |
| SH-52A | 54.126 | 87.107 | Payette River | SH-52 near Emmett | 01953-01-011953 | 01973-01-011973 | now Black Canyon Highway |
| SH-53 | 14.255 | 22.941 | SR 290 near State Line | US-95 near Hayden | 01938-01-011938 | current | |
| SH-54 | 15.440 | 24.848 | SH-41 in Spirit Lake | Main Avenue in Bayview | 01953-01-011953 | current | |
| SH-55 | — | — | US-2 in Colburn | US-10 Alternate near Kootenai | 01953-01-011953 | 01955-01-011955 | now Colburn-Culver Road |
| SH-55 | 156.047 | 251.133 | US-95 near Marsing | US-95 in New Meadows | 01967-01-011967 | current | |
| SH-56 | — | — | US-95 in Sagle | Garfield | 01953-01-011953 | 01955-01-011955 | now Sagle Road, Glengary Road, and Garfield Cutoff Road |
| SH-57 | 37.230 | 59.916 | US-2 in Priest River | Reeder Creek Road in Nordman | 01953-01-011953 | current | |
| SH-58 | 2.943 | 4.736 | SR 278 near Rockford, Washington | US-95 near Worley | 01953-01-011953 | current | |
| SH-60 | 5.510 | 8.867 | SR 274 near Tekoa, Washington | US-95 near Tensed | 01959-01-011959 | current | |
| SH-61 | 0.740 | 1.191 | WYO 89 near Geneva | US-89 in Geneva | 01953-01-011953 | current | |
| SH-62 | 15.410 | 24.800 | US-95 Business in Craigmont | SH-64 / SH-162 in Nezperce | 01953-01-011953 | current | |
| SH-64 | 15.409 | 24.798 | SH-62 / SH-162 in Nezperce | SH-162 in Kamiah | 01962-01-011962 | current | Originally continued west to Craigmont |
| SH-66 | 0.992 | 1.596 | Palouse Cove Road near Palouse, Washington | US-95 near Viola | 01953-01-011953 | current | |
| SH-67 | 8.948 | 14.400 | Mountain Home Air Force Base | SH-51 in Mountain Home | 01953-01-011953 | current | |
| SH-68 | — | — | US-30 in Mountain Home | US-20 Temp / US-26 in Carey | 01953-01-011953 | 01978-01-011978 | Replaced by rerouted US-20 |
| SH-69 | 8.012 | 12.894 | Orchard Avenue in Kuna | I-84 / US-30 / SH-55 in Meridian | 01953-01-011953 | current | |
| SH-70 | — | — | Eaton Road near Eaton | US-95 Business in Weiser | 01953-01-011953 | 01977-01-011977 | Now County Road 70 |
| SH-71 | 28.730 | 46.236 | US-95 in Cambridge | OR 86 near Brownlee Dam | 01956-01-011956 | current | |
| SH-72 | — | — | US-95 near Marsing | US-30 near Nampa | 01953-01-011953 | 01967-01-011967 | Renumbered as part of SH-55 |
| SH-72 | 1.989 | 3.201 | US-30 near New Plymouth | SH-52 at Hamilton Corner | 01972-01-011972 | current | Former alignment of US-30 |
| SH-73 | — | — | US-30 in Buhl | Castleford | 01953-01-011953 | 01953-01-011953 | Now 1400 East, 3700 North, 1200 East, and 3600 North |
| SH-73 | — | — | US-30 in New Plymouth | I-84 | 01965-01-011965 | 01972-01-011972 | Replaced by rerouted US-30 |
| SH-74 | 7.835 | 12.609 | US-93 near Knull | US-30 in Twin Falls | 01953-01-011953 | current | |
| SH-75 | — | — | US-93 in Ketchum | Sun Valley | 01953-01-011953 | 01977-01-011977 | For a time continued northeast to Chilly; redesignated as a spur of the current route |
| SH-75 | 170.666 | 274.660 | US-26 / US-93 in Shoshone | US-93 near Challis | 01977-01-011977 | current | Former alignment of US-93 |
| SH-76 | — | — | 1420 North north of Richfield | US-26 in Richfield | 01953-01-011953 | 01954-01-011954 | Now 3rd Street and Center Road |
| SH-77 | 30.676 | 49.368 | SH-81 in Malta | I-84 / SH-25 near Declo | 01953-01-011953 | current | |
| SH-78 | 99.720 | 160.484 | SH-55 in Marsing | I-84 Business in Hammett | 01972-01-011972 | current | |
| SH-79 | 2.564 | 4.126 | I-84 in Jerome | SH-25 in Jerome | 01953-01-011953 | current | |
| SH-80 | — | — | SH-48 in Menan | US-20 in Lorenzo | 01953-01-011953 | 01962-01-011962 | Now Menan-Lorenzo Highway |
| SH-81 | 33.978 | 54.682 | SH-77 in Malta | US-30 in Burley | 01970-01-011970 | current | |
| SH-84 | — | — | US-20 in Macks Inn | Big Springs | 01953-01-011953 | 01977-01-011977 | Now Big Springs Loop Road |
| SH-86 | — | — | West Side Highway (formerly SH-35) in Dayton | US-91 in Preston | 01953-01-011953 | 01964-01-011964 | Removed from the state highway system; restored in 1985 as part of SH-36 |
| SH-87 | 9.133 | 14.698 | US-20 in Island Park | MT 87 at Raynolds Pass | 01967-01-011967 | current | |
| SH-88 | — | — | US-20 / US-26 near Arco | US-20 in Rexburg | 01953-01-011953 | 01977-01-011977 | Replaced by SH-33 |
| SH-96 | 9.133 | 14.698 | US-20 in Island Park | MT 287 at Raynolds Pass | 01959-01-011959 | 01960-01-011960 | renumbered SH-287 to match Montana; later renumbered SH-87 on both sides of the border |
| SH-97 | 35.745 | 57.526 | SH-3 near Harrison | I-90 near Coeur d'Alene | 01977-01-011977 | current | |
| SH-99 | 11.686 | 18.807 | SH-3 in Kendrick | SH-8 in Troy | 01961-01-011961 | current | |
| SH-128 | 2.198 | 3.537 | SR 128 near Lewiston | US-12 in Lewiston | 01989-01-011989 | current | |
| SH-162 | 31.077 | 50.014 | SH-62 / SH-64 in Nezperce | US-12 in Kamiah | 01993-01-011993 | current | Former portion of SH-62 |
| SH-167 | 16.319 | 26.263 | SH-78 in Grand View | SH-67 near Mountain Home Air Force Base | 02010-01-012010 | current | Former portion of SH-67 |
| SH-200 | 33.169 | 53.380 | US-2 / US-95 in Ponderay | MT 200 near Clark Fork | 01967-01-011967 | current | Formerly U.S. Route 10 Alternate |
| SH-287 | 9.133 | 14.698 | US-20 in Island Park | MT 287 at Raynolds Pass | 01960-01-011960 | 01967-01-011967 | renumbered SH-87 when Montana renumbered Highway 287 to Highway 87 |