List of state highways in Idaho

	Highway markers for State Highways 3, 75 and 200
Highway names
Interstates	Interstate X (I-X)
US Highways	U.S. Route X (US-X)
System links
	Idaho State Highway System; Interstate; US; State;

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.^[1] The current state highway marker consists of a white background, black numbering, and a solid black geographic outline of the state of Idaho.

History

Marker design prior to 2020

Scenic state highway marker formerly used on Idaho State Highway 21

During the 1920s, in lieu of numbering its highways, Idaho had a system of lettered Sampson Trails.^[2] They were marked by businessman Charles B. Sampson of Boise at no expense to the state, using orange-colored shields.^[3] By 1929, the trails system had included 6,500 miles (10,500 km) of marked highways that covered most of the state.^[4] By the mid-1930s, the state had adopted a more standard system of numbered state highways.^[5]^[6]

In 1978, the ITD began using brown state highway markers to denote scenic Idaho highways,^[7] 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.^[8]

Sampson Trails

Rand McNally Atlas from 1926 showing the Sampson Trails as well as US Highways

The following Sampson Trails were marked:^[2]

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;^{[citation needed]} 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)^[9]	Length (km)	Southern or western terminus	Northern or eastern terminus	Formed^[10]	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