Feature Name | Class | Elev. meters | County | Latitude DMS | Longitude DMS |
| Our Lady of Lourdes Church | Church | 609 | Roosevelt | 48 06 50 N | 105 11 46 W |
| Our Lady of Lourdes School | School | 1025 | Cascade | 47 30 02 N | 111 17 02 W |
| Our Lady of Mercy Catholic Church | Church | 797 | Lincoln | 48 52 58 N | 115 03 14 W |
| Our Lady of Ransom Catholic Church | Church | 924 | Hill | 48 33 18 N | 110 25 20 W |
| Our Lady of the Assumption Church (historical) | Church | 1271 | Stillwater | 46 04 42 N | 109 01 46 W |
| Our Lady of the Bitterroot Chapel of the Society of Saint Pius X | Church | 1045 | Ravalli | 46 24 56 N | 114 09 16 W |
| Our Lady of the Pines Catholic Church | Church | 2031 | Gallatin | 44 39 40 N | 111 06 30 W |
| Our Lady of the Rockies | Park | 2390 | Silver Bow | 45 59 56 N | 112 26 46 W |
| Our Lady of the Valley Catholic Church | Church | 1133 | Lewis and Clark | 46 39 53 N | 112 01 06 W |
| Our Lady of Wisdom Mission | Church | 1844 | Beaverhead | 45 37 05 N | 113 27 03 W |
| Our Lake | Lake | 2220 | Teton | 47 50 12 N | 112 48 39 W |
| Our Only Chance Mine | Mine | 2264 | Judith Basin | 46 50 11 N | 110 36 24 W |
| Our Redeemer Lutheran Church | Church | 940 | Flathead | 48 22 20 N | 114 11 26 W |
| Our Redeemers Lutheran Church | Church | 1262 | Lewis and Clark | 46 35 56 N | 112 03 31 W |
| Our Redeemers Lutheran Church | Church | 630 | Valley | 48 08 04 N | 106 21 18 W |
| Our Savior Lutheran Church | Church | 627 | Dawson | 47 06 30 N | 104 42 54 W |
| Our Savior Lutheran Church | Church | 1128 | Hill | 48 15 22 N | 109 47 18 W |
| Our Savior Lutheran Church | Church | 949 | Hill | 48 33 36 N | 110 33 15 W |
| Our Savior Lutheran Church | Church | 955 | Liberty | 48 30 39 N | 110 57 56 W |
| Our Savior Lutheran Church | Church | 1030 | Ravalli | 46 29 14 N | 114 04 58 W |
| Our Saviors Cemetery | Cemetery | 683 | Sheridan | 48 58 07 N | 104 08 07 W |
| Our Saviors Church | Church | 887 | Valley | 48 37 18 N | 106 07 24 W |
| Our Saviors Episcopal Church | Church | 1139 | Carbon | 45 29 07 N | 108 58 14 W |
| Our Saviors Lutheran Church | Church | 1029 | Cascade | 47 30 22 N | 111 17 01 W |
| Our Saviors Lutheran Church | Church | 1097 | Fergus | 47 19 11 N | 109 56 51 W |
| Our Saviors Lutheran Church | Church | 942 | Flathead | 48 22 20 N | 114 11 03 W |
| Our Saviors Lutheran Church | Church | 1010 | Missoula | 46 52 24 N | 113 51 52 W |
| Our Saviors Lutheran Church | Church | 608 | Roosevelt | 48 09 05 N | 104 55 04 W |
| Our Saviors Lutheran Church | Church | 762 | Sanders | 47 35 48 N | 115 20 54 W |
| Our Saviors Lutheran Church (historical) | Church | 683 | Sheridan | 48 58 07 N | 104 08 07 W |
| Ousel Creek | Stream | | Flathead | 48 29 46 N | 113 53 11 W |
| Ousel Falls | Falls | 2016 | Gallatin | 45 14 21 N | 111 20 30 W |
| Ousel Falls Recreation Site | Locale | 2034 | Gallatin | 45 14 33 N | 111 20 24 W |
| Ousel Peak | Summit | 2179 | Flathead | 48 27 55 N | 113 53 15 W |
| Ousel Peak Trail | Trail | 2066 | Flathead | 48 26 56 N | 113 54 01 W |
| Ousley Mine | Mine | 2291 | Jefferson | 46 24 53 N | 112 14 03 W |
| Out Post Campground | Locale | 1003 | Missoula | 46 58 47 N | 114 07 23 W |
| Outback Mobile Home Settlement | Populated Place | 923 | Flathead | 48 24 40 N | 114 20 15 W |
| Outlaw Coulee | Valley | | Daniels | 48 59 35 N | 105 10 47 W |
| Outlaw Coulee | Valley | | Treasure | 46 05 26 N | 107 06 56 W |
| Outlaw Creek | Stream | | Sanders | 47 34 13 N | 115 10 34 W |
| Outlaw Lake | Lake | 1741 | Sanders | 47 32 56 N | 115 11 21 W |
| Outlaw Spring | Spring | 987 | Treasure | 46 04 03 N | 107 04 24 W |
| Outlet Creek | Stream | | Daniels | 48 58 04 N | 105 25 44 W |
| Outlet Marsh Waterfowl Production Area | Park | 750 | Daniels | 48 59 46 N | 105 18 44 W |
| Outlook | Locale | 714 | Sheridan | 48 53 13 N | 104 46 42 W |
| Outlook | Populated Place | 716 | Sheridan | 48 53 15 N | 104 46 40 W |
| Outlook General Hospital (historical) | Hospital | 720 | Sheridan | 48 53 22 N | 104 46 32 W |
| Outlook Post Office | Post Office | 720 | Sheridan | 48 53 22 N | 104 46 36 W |
| Outlook School | School | 716 | Sheridan | 48 53 24 N | 104 47 02 W |
| Ouzel Lake | Lake | 2875 | Carbon | 45 04 36 N | 109 47 19 W |
| Oval Lake | Lake | 2741 | Madison | 45 32 05 N | 112 01 52 W |
| Ovando | Populated Place | 1246 | Powell | 47 01 13 N | 113 07 59 W |
| Ovando Cemetery | Cemetery | 1261 | Powell | 47 01 04 N | 113 07 31 W |
| Ovando Elementary School | School | 1257 | Powell | 47 01 11 N | 113 07 42 W |
| Ovando Mountain | Summit | 2346 | Powell | 47 05 41 N | 113 02 24 W |
| Ovando Post Office | Post Office | 1246 | Powell | 47 01 13 N | 113 07 59 W |
| Ovens Dam | Dam | 940 | Toole | 48 23 24 N | 111 46 15 W |
| Ovens Reservoir | Reservoir | 940 | Toole | 48 23 24 N | 111 46 15 W |
| Over the Hill Reservoir Dam | Dam | 850 | Blaine | 48 46 30 N | 109 02 33 W |
| Overall Spring | Spring | 1011 | Powder River | 45 22 07 N | 106 04 32 W |
| Overfelt Gulch | Valley | | Sweet Grass | 45 45 11 N | 109 45 54 W |
| Overland Creek | Stream | | Jefferson | 46 22 46 N | 112 13 32 W |
| Overland Golf Course | Locale | 1246 | Sweet Grass | 45 49 53 N | 109 55 38 W |
| Overlook Mountain | Summit | 3122 | Gallatin | 45 24 20 N | 110 56 33 W |
| Overlook Recreation Area | Locale | 1215 | Lewis and Clark | 46 37 50 N | 111 42 47 W |
| Overnight Reservoir | Reservoir | 1670 | Beaverhead | 45 19 40 N | 112 43 32 W |
| Overnight Reservoir Dam | Dam | 1671 | Beaverhead | 45 19 42 N | 112 43 33 W |
| Overstreet (historical) | Locale | 1069 | Carbon | 45 25 60 N | 108 52 31 W |
| Overturf Gulch | Valley | | Ravalli | 46 02 40 N | 114 10 59 W |
| Overwhich Creek | Stream | | Ravalli | 45 40 30 N | 114 18 26 W |
| Overwhich Falls | Falls | 1986 | Ravalli | 45 43 07 N | 114 04 38 W |
| Ovis Lake | Lake | 2630 | Beaverhead | 45 29 12 N | 113 44 38 W |
| Ovis Lake | Lake | 2932 | Park | 45 04 41 N | 109 55 11 W |
| OW Ranch | Locale | 1071 | Big Horn | 45 08 12 N | 106 28 34 W |
| Owachikaysis Ridge | Ridge | 1487 | Hill | 48 13 06 N | 109 37 59 W |
| Owen Brothers Airport | Airport | 946 | Chouteau | 47 37 04 N | 110 05 35 W |
| Owen Ditch | Canal | 1551 | Beaverhead | 45 13 13 N | 112 37 59 W |
| Owen Point | Summit | 2342 | Ravalli | 46 22 05 N | 113 51 25 W |
| Owens (historical) | Locale | 696 | Custer | 46 33 25 N | 105 38 02 W |
| Owens Coulee | Valley | | Custer | 46 32 04 N | 106 00 55 W |
| Owings Creek | Stream | | Ravalli | 46 13 56 N | 114 11 21 W |
| Owl Creek | Stream | | Big Horn | 45 17 21 N | 107 21 00 W |
| Owl Creek | Stream | | Carter | 44 40 27 N | 103 28 48 W |
| Owl Creek | Stream | | Lincoln | 47 57 52 N | 115 20 32 W |
| Owl Creek | Stream | | Mineral | 46 49 17 N | 114 39 13 W |
| Owl Creek | Stream | | Missoula | 47 26 10 N | 113 37 05 W |
| Owl Creek | Stream | | Missoula | 47 06 55 N | 113 26 34 W |
| Owl Creek Packer Camp | Locale | 1247 | Missoula | 47 26 27 N | 113 36 21 W |
| Owl Gulch | Valley | | Lewis and Clark | 46 47 54 N | 111 51 02 W |
| Owl Head Canyon | Valley | | Blaine | 48 00 42 N | 108 39 51 W |
| Owl Lake | Lake | 2909 | Sweet Grass | 45 16 33 N | 110 06 01 W |
| Owl Peak | Summit | 2512 | Flathead | 47 39 47 N | 113 36 22 W |
| Owl Peak | Summit | 1543 | Lincoln | 47 59 30 N | 115 20 52 W |
| Owsley Slough | Stream | | Madison | 45 32 03 N | 112 20 45 W |
| Ox Bow Ranch Airport | Airport | 1108 | Lewis and Clark | 46 58 44 N | 112 00 20 W |
| Ox Creek | Stream | | Fergus | 47 20 47 N | 109 47 03 W |
| Ox Frame Gulch | Valley | | Fergus | 47 07 42 N | 109 12 17 W |
| Ox Yoke Coulee | Valley | | Big Horn | 45 25 26 N | 107 40 52 W |
| Ox Yoke Dam | Dam | 811 | Petroleum | 47 30 18 N | 108 08 14 W |
| Ox Yoke Ranch | Locale | 1729 | Park | 45 18 34 N | 110 54 58 W |
| Oxarart Dam | Dam | 666 | Phillips | 48 32 21 N | 107 31 49 W |
| Oxbow Bend | Bend | 1175 | Lewis and Clark | 46 56 31 N | 111 57 55 W |
| Oxbow Creek | Stream | | Sweet Grass | 45 46 29 N | 110 06 38 W |
| Oxbow Landing Strip | Airport | 1106 | Lewis and Clark | 46 58 44 N | 112 00 10 W |
| Oxbow Ranch | Locale | 1108 | Lewis and Clark | 46 58 43 N | 112 00 26 W |
| Oxford | Locale | 1348 | Wheatland | 46 35 30 N | 109 41 18 W |
| Oxford Post Office (historical) | Post Office | 1348 | Wheatland | 46 35 30 N | 109 41 18 W |
| Oxheart Coulee | Valley | | Teton | 47 42 41 N | 112 34 03 W |
| Oxide Mountain | Summit | 3051 | Park | 45 04 48 N | 109 50 24 W |