Contents

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

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]

The following Sampson Trails were marked:^[2]

• A, BoisetoWyoming via Twin Falls and Pocatello; became US-30 and US-30N
• B, BoisetoCanada via Lewiston and Coeur d'Alene; became US-30, US-30N, US-95, and SH-1
• C, PocatellotoMontana via Idaho Falls; became US-91 and US-191
• D, BoisetoNew Meadows via Banks; became SH-15 (today's SH-55)
• E, not on the 1926 map
• F, BoisetoBlackfoot via Stanley; became SH-21, SH-17, US-93 (today's SH-75), and SH-27
• G, Mountain HometoPicabo via Fairfield; became SH-22 (today's US-20)
• H, BlisstoTrude via Arco; became SH-24, SH-23, SH-22, SH-29, and an unnumbered road (today's US-20 and US-26)
• I, PioneertoIdaho Falls; became an unnumbered road
• J, NevadatoShoshone via Twin Falls; became US-93
• K, UtahtoMcCammon via Preston; became US-91
• L, not on the 1926 map
• M, WashingtontoMontana via Coeur d'Alene; became US-10
• N, Bonners FerrytoMontana;^{[citation needed]} became US-2
• O, OregontoCaldwell; became SH-49 and SH-18
• P, UtahtoDowney; became SH-36
• Q, DeclotoFairfield; became SH-25 and SH-46
• R, not on the 1926 map
• S, OregontoNampa; became unnumbered road and SH-45
• T, StartoGrimes Pass; became SH-16, unnumbered road, and SH-17
• U, UtahtoMontpelier; became SH-35
• V, HaileytoStanley; became US-93 (today's SH-75)
• W, not on the 1926 map
• X, not on the 1926 map
• Y, Bonners FerrytoCanada; became US-95

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 21atPorthill	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-90inWallace	National Forest Road No. 7623 at Burke	01929-01-011929	current
SH-5	19.140	30.803	US-95inPlummer	SH-3inSaint 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 270inMoscow	1st Street in Elk River	01929-01-011929	current
SH-9	—	—	US-95inSpalding	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-7inGreencreek	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-12inGreer	Forest Service Road No. 247 near Headquarters	01929-01-011929	current
SH-12	—	—	US-95 BusinessinCraigmont	SH-62inKamiah	01929-01-011929	01962-01-011962	Renumbered SH-64 because US-12 extended into Idaho
SH-13	26.390	42.471	US-95inGrangeville	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-30inBoise	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-52inEmmett	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-30inFruitland	US-30inCaldwell	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-95inParma	01953-01-011953	01975-01-011975	Now Wanstad Road and Roswell Road
SH-19	19.915	32.050	OR 201 near Homedale	I-84 BusinessinCaldwell	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-84inBoise	SH-75inStanley	01929-01-011929	current
SH-22	43.936	70.708	SH-33 near Howe	I-15inDubois	01929-01-011929	current	Originally continued west to Mountain Home
SH-23	—	—	US-93inShoshone	SH-22inCarey	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-30inHeyburn	US-93inShoshone	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-30inTwin Falls	01929-01-011929	01953-01-011953	Renumbered SH-74 because US-26 extended into Idaho
SH-27	7.835	12.609	US-93inChallis	US-91inBlackfoot	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-25inPaul	01950-01-011950	current
SH-28	135.645	218.299	SH-33 near Mud Lake	US-93inSalmon	01929-01-011929	current
SH-29	—	—	SH-27 (now US-26) in Arco	US-91inDubois	01929-01-011929	01938-01-011938	Replaced by SH-22
SH-29	—	—	US-91inIdaho 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-28inLeadore	Montana Secondary Highway 324atBannock 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-26inSwan Valley	SH-33inVictor	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-36inPreston	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-91inDowney	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-89inOvid	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-15inMalad City	01985-01-011985	current	Formerly part of SH-37
SH-39	52.924	85.173	I-86inAmerican Falls	US-26inBlackfoot	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-91inDowney	01972-01-011972	current
SH-41	39.058	62.858	I-90inPost Falls	US-2inOldtown	01931-01-011931	current
SH-42	—	—	SH-7inKendrick	US-12 near Spalding	01934-01-011934	01965-01-011965	Replaced by SH-3; originally continued north to Harvard
SH-43	—	—	SH-7inAhsahka	SH-42inKendrick	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-26atBeachs Corner	US-20inUcon	01978-01-011978	current
SH-44	23.089	37.158	I-84 near Caldwell	US-20 / US-26inGarden City	01934-01-011934	current
SH-45	17.985	28.944	SH-78atWalters Ferry	I-84 BusinessinNampa	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-20inAshton	Caribou-Targhee National Forest near Warm River	01958-01-011958	current
SH-48	24.409	39.282	I-15 near Roberts	US-26 BusinessinRirie	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 BusinessinMountain Home	01938-01-011938	current
SH-52	54.126	87.107	OR 52inPayette	SH-55inHorseshoe 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-41inSpirit Lake	Main Avenue in Bayview	01953-01-011953	current
SH-55	—	—	US-2inColburn	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-95inNew Meadows	01967-01-011967	current
SH-56	—	—	US-95inSagle	Garfield	01953-01-011953	01955-01-011955	now Sagle Road, Glengary Road, and Garfield Cutoff Road
SH-57	37.230	59.916	US-2inPriest 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-89inGeneva	01953-01-011953	current
SH-62	15.410	24.800	US-95 BusinessinCraigmont	SH-64 / SH-162inNezperce	01953-01-011953	current
SH-64	15.409	24.798	SH-62 / SH-162inNezperce	SH-162inKamiah	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-51inMountain Home	01953-01-011953	current
SH-68	—	—	US-30inMountain Home	US-20 Temp / US-26inCarey	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-55inMeridian	01953-01-011953	current
SH-70	—	—	Eaton Road near Eaton	US-95 BusinessinWeiser	01953-01-011953	01977-01-011977	Now County Road 70
SH-71	28.730	46.236	US-95inCambridge	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-52atHamilton Corner	01972-01-011972	current	Former alignment of US-30
SH-73	—	—	US-30inBuhl	Castleford	01953-01-011953	01953-01-011953	Now 1400 East, 3700 North, 1200 East, and 3600 North
SH-73	—	—	US-30inNew 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-30inTwin Falls	01953-01-011953	current
SH-75	—	—	US-93inKetchum	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-93inShoshone	US-93 near Challis	01977-01-011977	current	Former alignment of US-93
SH-76	—	—	1420 North north of Richfield	US-26inRichfield	01953-01-011953	01954-01-011954	Now 3rd Street and Center Road
SH-77	30.676	49.368	SH-81inMalta	I-84 / SH-25 near Declo	01953-01-011953	current
SH-78	99.720	160.484	SH-55inMarsing	I-84 BusinessinHammett	01972-01-011972	current
SH-79	2.564	4.126	I-84inJerome	SH-25inJerome	01953-01-011953	current
SH-80	—	—	SH-48inMenan	US-20inLorenzo	01953-01-011953	01962-01-011962	Now Menan-Lorenzo Highway
SH-81	33.978	54.682	SH-77inMalta	US-30inBurley	01970-01-011970	current
SH-84	—	—	US-20inMacks 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-91inPreston	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-20inIsland Park	MT 87atRaynolds Pass	01967-01-011967	current
SH-88	—	—	US-20 / US-26 near Arco	US-20inRexburg	01953-01-011953	01977-01-011977	Replaced by SH-33
SH-96	9.133	14.698	US-20inIsland Park	MT 287atRaynolds 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-3inKendrick	SH-8inTroy	01961-01-011961	current
SH-128	2.198	3.537	SR 128 near Lewiston	US-12inLewiston	01989-01-011989	current
SH-162	31.077	50.014	SH-62 / SH-64inNezperce	US-12inKamiah	01993-01-011993	current	Former portion of SH-62
SH-167	16.319	26.263	SH-78inGrand 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-95inPonderay	MT 200 near Clark Fork	01967-01-011967	current	Formerly U.S. Route 10 Alternate
SH-287	9.133	14.698	US-20inIsland Park	MT 287atRaynolds Pass	01960-01-011960	01967-01-011967	renumbered SH-87 when Montana renumbered Highway 287 to Highway 87

• List of Interstate Highways in Idaho
• List of U.S. Highways in Idaho

Wikimedia Commons has media related to State highways in Idaho.

• Idaho Transportation Department
• Road Signs of Idaho (archived April 27, 2004)
• Pend Oreille Scenic Byway