Feature Name | Class | Elev. meters | County | Latitude DMS | Longitude DMS |
| Thompson Gulch School (historical) | School | 1768 | Meagher | 46 32 50 N | 111 10 58 W |
| Thompson Lake | Lake | 2778 | Gallatin | 45 22 21 N | 111 22 25 W |
| Thompson Lake | Lake | 2421 | Granite | 46 22 58 N | 113 02 54 W |
| Thompson Lake | Lake | 2402 | Park | 45 10 24 N | 110 33 34 W |
| Thompson Lakes | Lake | 1016 | Lincoln | 48 02 13 N | 115 04 60 W |
| Thompson Park | Park | 1781 | Silver Bow | 45 53 07 N | 112 27 32 W |
| Thompson Park | Park | 1010 | Yellowstone | 45 40 34 N | 108 46 07 W |
| Thompson Pass | Gap | 1481 | Sanders | 47 34 38 N | 115 43 01 W |
| Thompson Peak | Summit | 3147 | Madison | 45 31 46 N | 112 01 16 W |
| Thompson Peak | Summit | 1318 | Mineral | 47 10 35 N | 114 55 08 W |
| Thompson Peak | Summit | 2270 | Sanders | 47 45 26 N | 114 50 46 W |
| Thompson Point | Cape | 983 | Sanders | 47 41 37 N | 115 29 15 W |
| Thompson Post Office (historical) | Post Office | 1768 | Meagher | 46 32 50 N | 111 10 58 W |
| Thompson Ranch | Locale | 1417 | Cascade | 47 05 60 N | 111 34 32 W |
| Thompson Ranch | Locale | 1426 | Jefferson | 45 53 46 N | 111 46 11 W |
| Thompson Ranch | Locale | 1275 | Liberty | 48 53 14 N | 111 13 20 W |
| Thompson Ranch | Locale | 1555 | Park | 45 59 28 N | 110 35 52 W |
| Thompson Reservoir | Reservoir | 2729 | Madison | 45 31 19 N | 112 01 24 W |
| Thompson River | Stream | | Sanders | 47 34 37 N | 115 14 23 W |
| Thompson River Mount Headley Trail | Trail | 2103 | Sanders | 47 45 14 N | 115 13 35 W |
| Thompson River School (historical) | School | 1041 | Flathead | 48 00 18 N | 114 58 34 W |
| Thompson River Spur | Locale | 746 | Sanders | 47 34 44 N | 115 13 54 W |
| Thompson River State Forest | Forest | 1036 | Sanders | 47 41 56 N | 114 58 29 W |
| Thompson School (historical) | School | 1102 | Fergus | 47 25 58 N | 109 50 31 W |
| Thompson School (historical) | School | 683 | Roosevelt | 48 29 00 N | 105 21 17 W |
| Thompson Spring | Spring | 1152 | Carter | 45 47 09 N | 104 34 39 W |
| Thompson Spring | Spring | 1684 | Madison | 45 08 58 N | 112 08 23 W |
| Thompson-Hickman County Library | Building | 1756 | Madison | 45 17 38 N | 111 56 46 W |
| Thompson-Hickman Museum | Building | 1778 | Madison | 45 17 38 N | 111 56 30 W |
| Thompsons River Post Office (historical) | Post Office | 740 | Sanders | 47 34 35 N | 115 14 49 W |
| Thompsons Ski Trail | Trail | 2528 | Carbon | 45 11 15 N | 109 21 03 W |
| Thompsons Water Hole | Spring | 1089 | Musselshell | 46 20 10 N | 108 33 37 W |
| Thomsen School (historical) | School | 688 | Roosevelt | 48 12 53 N | 104 27 42 W |
| Thora Number 2 Dam | Dam | 748 | McCone | 47 48 42 N | 106 08 26 W |
| Thorn Dam | Dam | 809 | McCone | 47 12 54 N | 105 52 02 W |
| Thornberg Lake | Lake | 1010 | Flathead | 48 27 54 N | 114 24 44 W |
| Thorne Creek | Stream | | Lake | 47 17 04 N | 114 03 42 W |
| Thorne Creek | Stream | | Sanders | 47 41 30 N | 115 24 02 W |
| Thornhill Butte | Summit | 1405 | Phillips | 47 51 25 N | 108 40 49 W |
| Thornquist Gulch | Valley | | Meagher | 46 43 12 N | 110 51 31 W |
| Thornton Creek | Stream | | Powell | 46 16 45 N | 112 59 25 W |
| Thornton Lake | Lake | 2311 | Granite | 46 15 33 N | 113 02 18 W |
| Thornton Lake | Reservoir | 2309 | Deer Lodge | 46 15 36 N | 113 02 03 W |
| Thornton Lake Dam | Dam | 2309 | Deer Lodge | 46 15 36 N | 113 02 03 W |
| Thornton Ridge | Ridge | 2622 | Deer Lodge | 46 15 18 N | 113 01 15 W |
| Thornwood Ranch | Locale | 686 | Roosevelt | 48 31 42 N | 104 46 36 W |
| Thornwood School (historical) | School | 676 | Sheridan | 48 36 09 N | 104 48 22 W |
| Thorpe Creek | Stream | | Custer | 46 09 22 N | 105 48 44 W |
| Thorpe Elevator (historical) | Locale | 786 | McCone | 47 18 04 N | 105 45 54 W |
| Thorsens Pond | Lake | 2000 | Meagher | 46 32 01 N | 110 37 22 W |
| Thorson School (historical) | School | 768 | Prairie | 46 49 27 N | 105 02 54 W |
| Three Acre Wood Ski Trail | Trail | 1816 | Lewis and Clark | 46 45 12 N | 112 18 50 W |
| Three Bar Creek | Stream | | Powder River | 45 00 38 N | 105 37 31 W |
| Three Bar Creek | Stream | | Powder River | 45 09 29 N | 105 46 27 W |
| Three Bar Ranch | Locale | 1110 | Powder River | 45 01 60 N | 105 40 26 W |
| Three Bears Bowl Ski Trail | Trail | 1863 | Gallatin | 45 49 02 N | 110 53 48 W |
| Three Bears Lake | Lake | 1611 | Glacier | 48 19 29 N | 113 21 50 W |
| Three Bears Traverse Ski Trail | Trail | 1863 | Gallatin | 45 49 02 N | 110 53 48 W |
| Three Brothers | Summit | 2604 | Jefferson | 46 23 29 N | 112 15 38 W |
| Three Buttes | Range | 1160 | Blaine | 48 10 34 N | 108 44 60 W |
| Three Buttes | Summit | 1254 | Fergus | 46 54 05 N | 108 39 38 W |
| Three Buttes | Summit | 963 | Garfield | 46 51 31 N | 106 40 26 W |
| Three Buttes | Summit | 1397 | Musselshell | 46 18 08 N | 108 13 52 W |
| Three Buttes | Summit | 1023 | Petroleum | 47 07 55 N | 108 43 29 W |
| Three Buttes | Summit | 830 | Richland | 47 43 57 N | 104 33 35 W |
| Three Buttes | Summit | 771 | Richland | 48 01 53 N | 104 25 32 W |
| Three Buttes | Summit | 702 | Valley | 48 08 33 N | 105 55 33 W |
| Three Buttes Creek | Stream | | Richland | 47 43 41 N | 104 30 14 W |
| Three Buttes Post Office (historical) | Post Office | 763 | Richland | 47 45 40 N | 104 31 05 W |
| Three Buttes School (historical) | School | 865 | Prairie | 47 09 43 N | 105 45 59 W |
| Three Cabins Creek | Stream | | Meagher | 46 45 50 N | 110 46 11 W |
| Three Chimney Coulee | Valley | | Valley | 48 44 12 N | 107 12 07 W |
| Three Circle Ranch | Locale | 955 | Rosebud | 45 20 14 N | 106 31 33 W |
| Three Corner Spring | Spring | 1410 | Carbon | 45 01 22 N | 109 08 60 W |
| Three Creeks | Stream | | Park | 45 27 37 N | 110 22 45 W |
| Three Dollar Bill Dam | Dam | 968 | Toole | 48 29 24 N | 111 33 03 W |
| Three Eagles Lakes | Lake | 1740 | Flathead | 48 07 15 N | 113 51 44 W |
| Three Eagles Mountain | Summit | 2270 | Flathead | 48 06 44 N | 113 52 13 W |
| Three Forks | Area | 788 | Valley | 48 27 46 N | 106 17 27 W |
| Three Forks | Locale | 1244 | Gallatin | 45 52 58 N | 111 33 06 W |
| Three Forks | Locale | 1722 | Ravalli | 45 45 24 N | 114 03 18 W |
| Three Forks | Populated Place | 1208 | Cascade | 47 16 54 N | 111 05 25 W |
| Three Forks | Populated Place | 1405 | Flathead | 48 06 49 N | 113 18 31 W |
| Three Forks | Populated Place | 1242 | Gallatin | 45 53 33 N | 111 33 08 W |
| Three Forks Airport | Airport | 1244 | Gallatin | 45 52 57 N | 111 33 53 W |
| Three Forks Community Library | Building | 1241 | Gallatin | 45 53 38 N | 111 32 58 W |
| Three Forks Cow Camp | Locale | 2037 | Madison | 44 54 35 N | 111 59 45 W |
| Three Forks Dam | Dam | 862 | Rosebud | 46 43 42 N | 106 40 26 W |
| Three Forks Fire Department | Building | 1242 | Gallatin | 45 53 35 N | 111 33 08 W |
| Three Forks Hospital (historical) | Hospital | 1242 | Gallatin | 45 53 33 N | 111 33 08 W |
| Three Forks Junction | Populated Place | 1257 | Broadwater | 45 53 55 N | 111 35 59 W |
| Three Forks KOA Kampground | Locale | 1276 | Broadwater | 45 54 10 N | 111 36 07 W |
| Three Forks of the Missouri Historical Marker | Park | 1239 | Gallatin | 45 54 10 N | 111 32 03 W |
| Three Forks Pack Bridge | Bridge | 1404 | Flathead | 48 06 47 N | 113 18 31 W |
| Three Forks Police Department | Building | 1242 | Gallatin | 45 53 33 N | 111 33 08 W |
| Three Forks Pond | Park | 1238 | Gallatin | 45 54 20 N | 111 32 13 W |
| Three Forks Ponds Fishing Access Site | Locale | 1238 | Gallatin | 45 53 42 N | 111 32 09 W |
| Three Forks Post Office | Post Office | 1242 | Gallatin | 45 53 37 N | 111 33 08 W |
| Three Forks Schools | School | 1241 | Gallatin | 45 53 48 N | 111 32 53 W |
| Three Hundred and Twenty Ranch | Locale | 1995 | Gallatin | 45 06 09 N | 111 12 49 W |
| Three Hundred Dam | Dam | 866 | Phillips | 48 56 18 N | 107 54 32 W |
| Three Islands | Island | 776 | Chouteau | 47 58 12 N | 110 22 09 W |
| Three Jim Ditch | Canal | 1485 | Madison | 45 46 44 N | 111 56 20 W |
| Three Lakes Community Bible Church | Church | 579 | Lincoln | 48 27 48 N | 115 53 23 W |
| Three Lakes Creek | Stream | | Lewis and Clark | 47 42 06 N | 113 03 22 W |
| Three Lakes Peak | Summit | 2356 | Sanders | 47 15 31 N | 114 33 45 W |
| Three Mile Creek | Stream | | Blaine | 48 33 39 N | 109 12 25 W |
| Three Mile Creek Mine | Mine | 1399 | Ravalli | 46 36 50 N | 113 53 03 W |
| Three Mile Reservoir Dam | Dam | 717 | Blaine | 48 26 12 N | 108 37 57 W |
| Three Mile Reservoir Dam | Dam | 1365 | Lewis and Clark | 46 41 48 N | 112 10 51 W |