Feature Name | Class | Elev. meters | County | Latitude DMS | Longitude DMS |
| Oriole | Populated Place | 251 | Perry | 38 10 08 N | 086 30 17 W |
| Oriole Lake | Reservoir | 239 | Perry | 38 11 06 N | 086 29 31 W |
| Orland | Populated Place | 291 | Steuben | 41 43 50 N | 085 10 18 W |
| Orlea Cemetery | Cemetery | 176 | Parke | 39 40 51 N | 087 18 17 W |
| Orleans | Populated Place | 193 | Orange | 38 39 42 N | 086 27 06 W |
| Orleans Airport | Airport | 195 | Orange | 38 39 30 N | 086 26 35 W |
| Orleans Elementary School | School | 191 | Orange | 38 39 43 N | 086 27 13 W |
| Orleans High School | School | 196 | Orange | 38 40 04 N | 086 27 16 W |
| Orleans Springs (historical) | Spring | 193 | Orange | 38 40 28 N | 086 26 52 W |
| Orleans Water Works Reservoir | Reservoir | 195 | Orange | 38 40 36 N | 086 26 54 W |
| Orleans Water Works Reservoir Dam | Dam | 195 | Orange | 38 40 36 N | 086 26 54 W |
| Ormas | Populated Place | 276 | Whitley | 41 17 42 N | 085 32 46 W |
| Orme Ditch | Canal | 201 | Marion | 39 38 48 N | 086 12 24 W |
| Ormes Cemetery | Cemetery | 305 | Rush | 39 33 48 N | 085 30 52 W |
| Orndorff Cemetery | Cemetery | 134 | Knox | 38 52 53 N | 087 27 25 W |
| Orr Cemetery | Cemetery | 304 | Delaware | 40 13 38 N | 085 15 18 W |
| Orr Lake | Lake | 243 | LaPorte | 41 37 12 N | 086 46 27 W |
| Orrville | Populated Place | 131 | Knox | 38 27 29 N | 087 41 10 W |
| Orrville Cemetery | Cemetery | 130 | Knox | 38 28 07 N | 087 40 50 W |
| Orrville Hills | Range | 138 | Knox | 38 27 20 N | 087 41 20 W |
| Orschell Overlook | Locale | 302 | Franklin | 39 28 15 N | 084 58 42 W |
| Orthodontic Strip | Airport | 241 | LaPorte | 41 35 15 N | 086 54 10 W |
| Ortleib Lake | Reservoir | 208 | Brown | 39 09 01 N | 086 10 19 W |
| Osborn | Populated Place | 183 | Lake | 41 35 33 N | 087 28 08 W |
| Osborn Cemetery | Cemetery | 287 | LaGrange | 41 35 52 N | 085 27 31 W |
| Osborn Ditch | Canal | 283 | Boone | 40 08 08 N | 086 23 14 W |
| Osborn Ditch | Canal | 253 | Marion | 39 52 03 N | 085 58 30 W |
| Osborn Landing | Populated Place | 253 | Kosciusko | 41 16 52 N | 085 47 49 W |
| Osborn Manning Ditch | Canal | 232 | Elkhart | 41 42 23 N | 086 01 04 W |
| Osborn Prairie Church | Church | 204 | Fountain | 40 10 16 N | 087 16 54 W |
| Osborne Cemetery | Cemetery | 212 | Jasper | 40 55 23 N | 086 57 18 W |
| Osborne Lakes | Lake | 343 | Wayne | 39 59 09 N | 085 04 37 W |
| Osborne Spring | Spring | 181 | Greene | 38 56 32 N | 086 45 50 W |
| Osceola | Populated Place | 225 | St. Joseph | 41 39 54 N | 086 04 33 W |
| Osceola Elementary School | School | 225 | St. Joseph | 41 39 52 N | 086 04 30 W |
| Osco Run | Stream | | Rush | 39 38 56 N | 085 30 55 W |
| Oser Creek | Stream | | Wayne | 39 52 37 N | 085 07 01 W |
| Oser Reservoir | Reservoir | 284 | Ripley | 39 16 50 N | 085 13 25 W |
| Osgood | Populated Place | 300 | Ripley | 39 07 45 N | 085 17 30 W |
| Osgood Elementary School | School | 297 | Ripley | 39 07 45 N | 085 17 18 W |
| Osgood Field | Airport | 262 | Hancock | 39 44 52 N | 085 48 26 W |
| Osolo Elementary School | School | 235 | Elkhart | 41 42 55 N | 085 54 15 W |
| Osolo Township Ditch | Canal | 233 | Elkhart | 41 43 07 N | 085 57 26 W |
| Ossian | Populated Place | 256 | Wells | 40 52 50 N | 085 09 59 W |
| Ossian Elementary School | School | 256 | Wells | 40 52 40 N | 085 09 55 W |
| Oswego | Populated Place | 259 | Kosciusko | 41 19 13 N | 085 47 14 W |
| Oswego Lake | Reservoir | 255 | Kosciusko | 41 19 35 N | 085 47 10 W |
| Otis | Populated Place | 229 | LaPorte | 41 35 57 N | 086 54 21 W |
| Otis Ditch | Canal | 204 | Jasper | 41 09 41 N | 087 15 17 W |
| Otis Ditch | Canal | 200 | Jasper | 41 11 10 N | 087 14 44 W |
| Otis E Brown Elementary School | School | 221 | Marion | 39 44 54 N | 086 07 41 W |
| Otis Park | Park | 163 | Lawrence | 38 51 34 N | 086 27 16 W |
| Otis-Boyle Ditch | Canal | 206 | Newton | 41 09 27 N | 087 16 36 W |
| Otisco | Populated Place | 205 | Clark | 38 32 32 N | 085 40 02 W |
| Otsego Center | Populated Place | 294 | Steuben | 41 34 21 N | 084 54 32 W |
| Otsego Center Cemetery | Cemetery | 288 | Steuben | 41 34 08 N | 084 54 30 W |
| Otter Creek | Stream | | Bartholomew | 39 13 04 N | 085 48 32 W |
| Otter Creek | Stream | | Crawford | 38 17 15 N | 086 29 18 W |
| Otter Creek | Stream | | LaPorte | 41 43 32 N | 086 51 47 W |
| Otter Creek | Stream | | Ripley | 38 59 00 N | 085 36 18 W |
| Otter Creek | Stream | | Vigo | 39 33 59 N | 087 24 07 W |
| Otter Creek | Stream | | Wabash | 40 58 48 N | 085 49 38 W |
| Otter Creek | Stream | | Warrick | 38 00 47 N | 087 10 09 W |
| Otter Creek Cemetery | Cemetery | 254 | Jennings | 39 04 20 N | 085 28 22 W |
| Otter Creek Church | Church | 246 | Putnam | 39 37 35 N | 087 00 45 W |
| Otter Creek Church | Church | 188 | Vigo | 39 32 29 N | 087 13 24 W |
| Otter Creek Church | Church | 128 | Warrick | 38 05 42 N | 087 12 16 W |
| Otter Creek Junction | Populated Place | 154 | Vigo | 39 32 47 N | 087 20 54 W |
| Otter Creek Junior High School | School | 149 | Vigo | 39 31 27 N | 087 22 16 W |
| Otter Lake | Lake | 285 | Steuben | 41 38 09 N | 085 10 06 W |
| Otter Pond | Reservoir | 123 | Knox | 38 38 46 N | 087 32 53 W |
| Otter Village | Populated Place | 292 | Ripley | 39 07 07 N | 085 19 53 W |
| Otter Village Cemetery | Cemetery | 288 | Ripley | 39 07 20 N | 085 20 58 W |
| Otterbein | Populated Place | 215 | Tippecanoe | 40 29 26 N | 087 05 47 W |
| Otterbein Church | Church | 241 | Cass | 40 38 44 N | 086 12 15 W |
| Otterbein Church | Church | 265 | Hancock | 39 48 46 N | 085 51 26 W |
| Otterbein Church | Church | 185 | Harrison | 38 01 24 N | 086 09 06 W |
| Otterbein Church | Church | 193 | Owen | 39 20 32 N | 087 00 44 W |
| Otterbein Church | Church | 222 | Parke | 39 43 47 N | 087 06 19 W |
| Otterbein Ditch | Canal | 213 | Tippecanoe | 40 29 16 N | 087 05 01 W |
| Otterbein Elementary School | School | 215 | Benton | 40 29 28 N | 087 05 52 W |
| Otterbein United Methodist Church | Church | 245 | Marion | 39 47 45 N | 086 05 07 W |
| Otto | Populated Place | 231 | Clark | 38 34 15 N | 085 28 01 W |
| Otwell | Populated Place | 152 | Pike | 38 27 17 N | 087 05 32 W |
| Otwell Cemetery | Cemetery | 265 | Franklin | 39 19 25 N | 084 49 39 W |
| Otwell Elementary School | School | 146 | Pike | 38 26 23 N | 087 05 32 W |
| Otwell Holiness Camp | Park | 145 | Pike | 38 26 10 N | 087 05 05 W |
| Ouabache State Park | Park | 259 | Wells | 40 43 22 N | 085 06 24 W |
| Ouiatenon Blockhouse | Building | 161 | Tippecanoe | 40 24 23 N | 086 57 50 W |
| Our Lady of Consolation Church | Church | 213 | Lake | 41 28 03 N | 087 21 49 W |
| Our Lady of Grace Church | Church | 188 | Lake | 41 33 21 N | 087 27 18 W |
| Our Lady of Grace School | School | 235 | Hamilton | 40 03 11 N | 086 00 41 W |
| Our Lady of Grace School | School | 187 | Lake | 41 33 22 N | 087 27 21 W |
| Our Lady of Grace School | School | 243 | Marion | 39 43 55 N | 086 05 55 W |
| Our Lady of Guadalupe Roman Catholic Church | Church | 181 | Lake | 41 38 53 N | 087 26 47 W |
| Our Lady of Hungary School | School | 235 | St. Joseph | 41 39 12 N | 086 15 37 W |
| Our Lady of Lourdes Roman Catholic Church | Church | 246 | Marion | 39 46 11 N | 086 04 41 W |
| Our Lady of Lourdes School | School | 246 | Marion | 39 46 10 N | 086 04 41 W |
| Our Lady of Mount Carmel School | School | 269 | Hamilton | 39 59 55 N | 086 08 54 W |
| Our Lady of Perpetual Help Church | Church | 183 | Lake | 41 34 59 N | 087 27 35 W |
| Our Lady of Perpetual Help Church (historical) | Church | 183 | Lake | 41 36 00 N | 087 20 30 W |
| Our Lady of Perpetual Help School | School | 146 | Floyd | 38 19 13 N | 085 48 29 W |
| Our Lady of Perpetual Help School | School | 183 | Lake | 41 35 03 N | 087 27 35 W |
| Our Lady of Providence High School | School | 139 | Clark | 38 18 23 N | 085 47 02 W |
| Our Lady of the Lake Seminary | School | 259 | Kosciusko | 41 24 47 N | 085 42 01 W |
| Our Lord Jesus Christ the King Catholic Church | Church | 227 | Marion | 39 51 43 N | 086 07 44 W |
| Our Redeemer Evangelical Lutheran Church | Church | 219 | Marion | 39 49 05 N | 086 08 50 W |
| Our Run | Stream | | Wayne | 39 52 20 N | 085 03 43 W |
| Our Savior Church | Church | 122 | Posey | 37 57 32 N | 087 28 21 W |
| Our Savior Lutheran Church | Church | 199 | Lake | 41 32 12 N | 087 20 42 W |