Wikipedia:WikiProject U.S. Roads/Idaho/highway names
Most information is from the meeting minutes and 1923 and 1925 maps (the latter bolded below).
- Alexander-Lund-Bancroft Road
- Ammon Spur: Idaho Falls to Ammon, removed 1953
- Arrow-Deary-Harvard Highway? SH-42: Spalding to Harvard
- Ashton-Drummond-Tetonia Road SH-32
- 32 Bannock Highway SH-38: Holbrook to Pocatello
- 36 Bear Lake Highway SH-35: Utah to Montpelier
- Beeches Corner South Road
- Bellevue-Gannett Highway
- Boise-Stanley Highway SH-21: Boise to Stanley
- Former 1 Arrowrock Highway: Boise to Arrowrock
- Former 35 Forest Highway: Lowman? to Stanley
- Boise Valley Highway: included Desert Junction-Middleton
- Bruneau-Duck Valley Highway
- Buhl-Castleford Highway SH-73: included Buhl southwest
- Canyon Highway SH-4: Wallace to Montana
- 3 Camas Prairie Highway? SH-13: Grangeville to Kooskia
- 5 Clark Fork Highway SH-3: Sandpoint to Montana
- 6 Clearwater Highway SH-11: Greer to Montana
- 23 Coeur d'Alene-Yellowstone Trail US-10: Washington to Montana
- Craigmont-Kamiah Highway?? SH-12: Craigmont to Kamiah
- Former 24A Nez Perce Branch of the North and South Highway: Craigmont to Nezperce
- Colburn Culver Road (SH 55):
- Cooley Road
- Cotton East Road
- Cub River Road
- Dayton-Red Rock Road (SH 35): included Oxford-Red Rock
- Deary-Bovill Road
- Declo-Albion Highway, formerly 4 Cassia Highway SH-77: Albion to Declo
- Dufort Road
- East Branch Road SH-57: included Priest River-Coolin
- East-West Road? included Fairfield
- 7 Elk City Highway SH-14: Harpster to Elk City
- 8 Elk River Highway SH-7: Orofino to Santa
- 34 Elk River Extension SH-7: Nezperce to Orofino
- Enaville-Murray Highway
- Fairfield-East Road
- Fairfield-West Road
- First Street-Iona Road
- Genesee-Thorn Creek Road?
- Georgetown-Nounan Road
- Glenns Ferry-East Road
- Gooding-Fairfield Road?
- 10 Grace-Preston Highway SH-34: Preston to Alexander
- Grace-Turner Road
- Grangeville-Craigmont Road
- Grangeville-Harvard Highway: included Harvard-Deary
- 11 Gray's Lake Highway SH-34: Soda Springs to Wyoming (earlier Soda Springs to Idaho Falls)
- Green Creek Junction-Reservation Line Road
- 12 Heyburn Park Highway SH-5: Plummer to St. Maries
- 13 Idaho Central Highway SH-22: Mountain Home to Trude
- 14 Idaho-Montana Highway US-91: Idaho Falls to Montana
- 15 Idaho-Oregon Highway SH-19: Oregon to Caldwell
- Ketchum-Clayton Highway (appears to be another name for part of the Sawtooth Park Highway)
- 38 Kootenai Highway US-2: Bonners Ferry to Idaho
- 18 Lemhi Highway SH-28: Roberts to Salmon
- 19 Lewis and Clark Highway[disambiguation needed] SH-9: Washington to Montana
- Lewiston-Orchards Road is another name for Thain Road.
- 20 Lost River Highway SH-27: Challis to Moreland
- 21 Malad Valley Highway SH-36 → US-191: Utah to Downey
- McCammon-Robin Road: included Robin-Arimo
- Middleton-South Road
- Minidoka-Kimama Road?
- Montour-Ola Road: included Sweet-Ola
- 22 Moscow-Bovill Highway SH-8: Moscow to Bovill
- Mountain Home-Grandview Road: included Grandview east
- Nampa Road: included Boise-Nampa (US 30)
- Nez Perce Highway SH-62: included Craigmont-Mohler
- North Bench Road
- 9 North Side Highway SH-25: Gooding to Rupert (earlier Declo?)
- 24 North and South Highway US-95, US-95A: Weiser to Canada
- Copeland-Porthill Branch SH-1: Copeland to Canada
- North Yellowstone Highway?
- 16 Old Oregon Trail Highway US-30, US-30N: Oregon to Wyoming
- 17 Ontario Branch US-30: Oregon to Fruitland
- 40 Southern Branch US-95, SH-18: Fruitland to Blacks Creek
- 41 Bancroft Loop: Lava Hot Springs to Lund
- 33 Oneida Highway SH-37: Malad to American Falls
- Ora Road: included west from Ashton
- 25 Owyhee Highway US-95, SH-20: Oregon to Nampa
- 37 Palouse Highway US-95: Potlatch to Coeur d'Alene
- Parma-Wilder Highway
- 26 Payette Highway SH-15: Boise to New Meadows
- Emmett Branch SH-16: Emmett to Horseshoe Bend
- Payette-Emmett Highway SH-16: Payette to Emmett, branch to New Plymouth
- Former? Emmett-New Plymouth Highway: Emmett to New Plymouth
- Pine Creek Road
- Pingree-Thomas Road
- Preston-Bear River Highway
- Priest River Road SH-57:
- Reservation Line Road
- Rexburg-Parker-St. Anthony Road: included Parker south
- Ririe-Beeches Corner Road
- Roberts-Ririe Highway SH-48: Roberts to Ririe
- Roberts West Road
- Robin West Road
- Rock Creek Road (SH 47): east of Ashton to Wyoming (Cave Falls Road), removed 1951
- 27 Roosevelt Highway SH-24, SH-39, SH-29: Bliss to Wyoming
- Former 2 Bliss-Shoshone Highway: Gooding to Shoshone
- Round Valley-Cascade Road
- Sagle-Midas Road (SH 56):
- Salmon River Highway?
- Salmon River North Highway?: included Riggins-Whitebird
- Samaria Lane Road
- 28 Sawtooth Park Highway US-93: Nevada to Montana
- Blue Lakes Spur: Kimberly Road to Addison Avenue in Twin Falls, created 1953
- Richfield Branch SH-23, SH-22: Shoshone to Bellevue
- Richfield Spur (SH 76):
- Twin Falls Loop SH-26: Godwin to Twin Falls
- Schiller-Arbon Valley Road?
- Sharon-Ovid Road
- Shelley-New Sweden Road
- South Yellowstone Highway SH-33: Rexburg to Wyoming
- Spirit Lake Highway SH-41: included Ross Point-Rathdrum
- 39 State Line Highway SH-40: Wyoming to Wyoming via Geneva
- 29 Teton Highway SH-32: Tetonia to Ashton
- Thain Road: Lewiston to Richardson Avenue, removed 1951
- Tin Cup Road
- Triumph Mine Road: Gimlet east, removed 1951
- 30 Twin Buttes Highway US-20: Arco to Idaho Falls
- Ucon-West Road
- Victor-Irwin Highway
- Wapello to Firth Road
- Wayan to Freedom Road
- Wood River Road
- Worley-State Line Highway SH-58: Washington to Worley
- 31 Yellowstone Park Highway US-91, US-191: Utah to Montana
- Yellowstone-Sun Valley Highway
What was the name of SH-6, Washington to Potlatch?