Feature Name | Class | Elev. meters | County | Latitude DMS | Longitude DMS |
| Onion Rock | Bar | 6 | Multnomah | 45 32 32 N | 122 16 08 W |
| Onion Spring | Spring | 1943 | Baker | 44 18 08 N | 118 20 59 W |
| Onion Spring | Spring | 1559 | Josephine | 42 41 34 N | 123 13 54 W |
| Onion Spring | Spring | 1664 | Klamath | 42 11 14 N | 122 10 43 W |
| Onion Spring | Spring | 1657 | Klamath | 42 36 11 N | 122 16 00 W |
| Onion Springs | Spring | 1472 | Jackson | 42 42 19 N | 123 13 24 W |
| Only Entry Point | Locale | 1270 | Union | 45 12 35 N | 118 30 06 W |
| Ontario | Populated Place | 656 | Malheur | 44 01 36 N | 116 57 47 W |
| Ontario Heights | Populated Place | 718 | Malheur | 44 04 14 N | 117 01 25 W |
| Ontario Heights Church | Church | 731 | Malheur | 44 04 08 N | 117 02 37 W |
| Ontario High School | School | 663 | Malheur | 44 01 48 N | 116 58 41 W |
| Ontario Island | Island | 653 | Malheur | 44 02 44 N | 116 57 54 W |
| Ontario Junior High School | School | 656 | Malheur | 44 01 36 N | 116 58 10 W |
| Ontario Municipal Airport | Airport | 668 | Malheur | 44 01 17 N | 117 00 48 W |
| Ontario Municipal Golf Course | Locale | 665 | Malheur | 44 01 10 N | 117 00 59 W |
| Ontario Nyssa Canal | Canal | 700 | Malheur | 43 53 48 N | 117 02 15 W |
| Ontario Post Office | Post Office | 656 | Malheur | 44 01 30 N | 116 57 50 W |
| Ontario Safety Rest Area | Locale | 655 | Malheur | 44 00 60 N | 116 56 41 W |
| Ontario State Park | Park | 655 | Malheur | 44 02 40 N | 116 58 14 W |
| Opal Butte | Summit | 1528 | Morrow | 45 02 38 N | 119 36 48 W |
| Opal City | Populated Place | 872 | Jefferson | 44 26 40 N | 121 12 49 W |
| Opal City Post Office (historical) | Post Office | 872 | Jefferson | 44 26 40 N | 121 12 49 W |
| Opal City School (historical) | School | 881 | Jefferson | 44 26 54 N | 121 11 57 W |
| Opal Creek | Stream | | Hood River | 45 35 52 N | 121 52 22 W |
| Opal Creek | Stream | | Jefferson | 44 34 27 N | 120 36 48 W |
| Opal Creek | Stream | | Marion | 44 50 33 N | 122 12 11 W |
| Opal Creek Trail | Trail | | Marion | 44 50 22 N | 122 12 03 W |
| Opal Creek Wilderness | Reserve | 1069 | Marion | 44 51 56 N | 122 14 35 W |
| Opal Lake | Lake | 1633 | Douglas | 43 25 15 N | 122 07 19 W |
| Opal Lake | Lake | 1031 | Marion | 44 47 36 N | 122 13 09 W |
| Opal Lake Recreation Site | Locale | 1646 | Douglas | 43 25 22 N | 122 07 24 W |
| Opal Mine Draw | Valley | | Baker | 44 26 50 N | 117 26 27 W |
| Opal Mountain | Summit | 1671 | Jefferson | 44 34 21 N | 120 33 38 W |
| Opal Pool | Lake | | Marion | 44 50 43 N | 122 12 32 W |
| Opal Reservoir | Reservoir | 1710 | Malheur | 42 03 37 N | 118 06 11 W |
| Opal Spring | Spring | 1277 | Morrow | 45 03 27 N | 119 33 06 W |
| Opal Springs | Spring | 661 | Jefferson | 44 29 26 N | 121 17 50 W |
| Opal Valley | Basin | 1263 | Malheur | 43 01 41 N | 118 08 03 W |
| Opalite Mine | Mine | 1630 | Malheur | 42 03 09 N | 118 02 07 W |
| Open Draw | Valley | | Harney | 42 55 41 N | 119 30 37 W |
| Open Triangle Tee Ranch | Locale | 1052 | Jackson | 42 00 43 N | 122 17 35 W |
| Open Valley | Valley | | Harney | 43 02 49 N | 119 25 09 W |
| Open Valley Waterhole | Spring | 1564 | Harney | 43 00 11 N | 119 25 57 W |
| Open Valley Waterhole Number Three | Lake | 1552 | Harney | 43 01 57 N | 119 25 43 W |
| Ophir | Populated Place | 11 | Curry | 42 33 47 N | 124 22 58 W |
| Ophir Beach | Beach | 25 | Curry | 42 32 59 N | 124 23 39 W |
| Ophir Mine | Mine | 2125 | Grant | 44 51 31 N | 118 19 37 W |
| Ophir Mine | Mine | 1891 | Grant | 44 42 41 N | 118 29 07 W |
| Ophir Mountain | Summit | 1193 | Curry | 42 39 22 N | 124 08 13 W |
| Ophir Post Office | Post Office | 11 | Curry | 42 33 47 N | 124 22 58 W |
| Ophir Safety Rest Area | Locale | 16 | Curry | 42 32 09 N | 124 23 59 W |
| Opie Dilldock Pass | Gap | 2112 | Lane | 44 11 26 N | 121 47 30 W |
| Oppenlander Field | Park | 210 | Clackamas | 45 22 07 N | 122 38 28 W |
| Optimism Reservoir | Reservoir | 1554 | Malheur | 42 24 48 N | 117 16 36 W |
| Ora Bolmeier City Park | Park | 211 | Columbia | 45 51 31 N | 123 11 05 W |
| Ora Creek | Stream | | Clackamas | 44 54 39 N | 122 09 58 W |
| Oral Hull Picnic Area | Locale | 216 | Clackamas | 45 23 59 N | 122 13 10 W |
| Orange Creek | Stream | | Grant | 44 15 35 N | 119 15 52 W |
| Orcal (historical) | Locale | 876 | Jackson | 42 00 17 N | 122 38 43 W |
| Orchard Bar | Bar | 14 | Curry | 42 29 29 N | 124 18 32 W |
| Orchard Creek | Stream | | Linn | 44 27 51 N | 122 43 44 W |
| Orchard Dale (historical) | Locale | 133 | Washington | 45 37 14 N | 123 13 04 W |
| Orchard Heights City Park | Park | 53 | Polk | 44 57 26 N | 123 03 41 W |
| Orchard Park | Park | 46 | Washington | 45 32 02 N | 122 53 32 W |
| Orchard Point | Cape | 116 | Lane | 44 06 44 N | 123 16 39 W |
| Orchard Point County Park | Park | 115 | Lane | 44 06 44 N | 123 16 38 W |
| Orchard Ridge Ditch | Canal | 688 | Wasco | 45 23 24 N | 121 17 24 W |
| Orchard View | Locale | 143 | Yamhill | 45 14 25 N | 123 16 16 W |
| Orchid Camp | Locale | 133 | Wasco | 45 34 32 N | 121 13 24 W |
| Ord Post Office (historical) | Post Office | 313 | Lane | 43 56 53 N | 123 47 54 W |
| Ordell Ditch | Canal | 827 | Union | 45 23 04 N | 118 02 03 W |
| Ordnance | Locale | 179 | Umatilla | 45 48 14 N | 119 25 00 W |
| Ordnance Post Office (historical) | Post Office | 179 | Umatilla | 45 48 14 N | 119 25 00 W |
| Ore Creek | Stream | | Lane | 44 14 01 N | 122 16 41 W |
| Oreana Creek | Stream | | Harney | 42 05 46 N | 118 29 22 W |
| Oreana Reservoir | Reservoir | 1609 | Harney | 42 10 08 N | 118 54 43 W |
| Oreana Waterhole | Reservoir | 1424 | Harney | 42 44 15 N | 119 19 24 W |
| Oredson Todd Woods | Park | | Jackson | 42 10 01 N | 122 40 44 W |
| Oregon Agricultural Experiment Station | Locale | 185 | Wasco | 45 37 16 N | 121 00 40 W |
| Oregon Agricultural Experimental Station | Locale | 1260 | Harney | 43 31 09 N | 119 01 17 W |
| Oregon Bar | Bar | 642 | Josephine | 42 07 49 N | 123 27 49 W |
| Oregon Belle Creek | Stream | | Jackson | 42 17 50 N | 123 04 37 W |
| Oregon Belle Mine | Mine | 1007 | Jackson | 42 17 27 N | 123 06 11 W |
| Oregon Bonanza Mine | Mine | 740 | Josephine | 42 16 48 N | 123 17 15 W |
| Oregon Butte | Summit | 1965 | Malheur | 42 00 43 N | 117 21 09 W |
| Oregon Butte Spring | Spring | 1896 | Malheur | 42 01 02 N | 117 20 13 W |
| Oregon Canyon | Valley | | Malheur | 42 13 43 N | 117 58 34 W |
| Oregon Canyon Creek | Stream | | Malheur | 42 02 57 N | 117 46 35 W |
| Oregon Canyon Mountains | Range | 1962 | Malheur | 42 09 60 N | 117 57 34 W |
| Oregon Canyon Ranch | Locale | 1527 | Malheur | 42 13 54 N | 117 55 46 W |
| Oregon Canyon Reservoir | Reservoir | 1549 | Malheur | 42 18 23 N | 117 58 11 W |
| Oregon Canyon Reservoir Number Two | Reservoir | 1606 | Malheur | 42 18 27 N | 117 58 50 W |
| Oregon Cascades Recreation Area | Locale | 1599 | Douglas | 43 14 58 N | 122 07 35 W |
| Oregon Caves National Monument | Park | 1330 | Josephine | 42 05 44 N | 123 24 21 W |
| Oregon Caves Post Office (historical) | Post Office | 1124 | Josephine | 42 05 53 N | 123 24 47 W |
| Oregon Caves Trail | Trail | 1354 | Josephine | 42 07 32 N | 123 22 57 W |
| Oregon Chief Mine | Mine | 1506 | Baker | 44 25 26 N | 117 32 36 W |
| Oregon Chief Mine | Mine | 2252 | Baker | 44 51 01 N | 118 17 08 W |
| Oregon City | Populated Place | 42 | Clackamas | 45 21 26 N | 122 36 24 W |
| Oregon City Airpark | Airport | 92 | Clackamas | 45 16 39 N | 122 35 49 W |
| Oregon City Golf Club | Locale | 160 | Clackamas | 45 18 54 N | 122 32 54 W |
| Oregon City High School | School | 75 | Clackamas | 45 21 24 N | 122 35 46 W |
| Oregon City Hospital | Hospital | 15 | Clackamas | 45 21 47 N | 122 36 01 W |
| Oregon City Post Office | Post Office | 128 | Clackamas | 45 19 35 N | 122 34 57 W |
| Oregon City Water Patrol Station | Locale | 212 | Clackamas | 45 11 54 N | 122 13 34 W |
| Oregon Coast Log Pond | Reservoir | 70 | Curry | 42 04 45 N | 124 18 42 W |
| Oregon Desert | Plain | 1849 | Klamath | 42 44 45 N | 122 11 26 W |
| Oregon Dunes National Recreation Area | Park | -9 | Coos | 43 41 59 N | 124 12 04 W |
| Oregon Dunes National Recreation Area Headquarters | Building | 5 | Douglas | 43 42 13 N | 124 06 21 W |
| Oregon Dunes Recreation Site | Locale | 38 | Douglas | 43 49 54 N | 124 08 59 W |