Feature Name | Class | Elev. meters | County | Latitude DMS | Longitude DMS |
| Nugent-Schpanski Number 4 Dam | Dam | 205 | Jersey | 39 00 54 N | 090 26 54 W |
| Nugent-Schpanski Number 4 Lake | Reservoir | 205 | Jersey | 39 00 54 N | 090 26 54 W |
| Nugent-Schpanski Number 6 Dam | Dam | 230 | Jersey | 38 59 54 N | 090 25 36 W |
| Nugent-Schpanski Number 6 Lake | Reservoir | 230 | Jersey | 38 59 54 N | 090 25 36 W |
| Number 1 Shaft Eureka Mine | Mine | 127 | Hardin | 37 27 00 N | 088 20 19 W |
| Number 10 School | School | 244 | Boone | 42 12 41 N | 088 43 36 W |
| Number 16 School (historical) | School | 243 | Knox | 41 01 31 N | 090 03 12 W |
| Number 2 Mine | Mine | 142 | Perry | 38 02 33 N | 089 14 31 W |
| Number 2 Portal Lake | Reservoir | 154 | Jefferson | 38 12 30 N | 089 06 36 W |
| Number 2 Portal Lake Dam | Dam | 154 | Jefferson | 38 12 30 N | 089 06 36 W |
| Number 4 School (historical) | School | 132 | Wayne | 38 28 56 N | 088 12 11 W |
| Number 6 Shaft Eureka Mine | Mine | 142 | Hardin | 37 26 49 N | 088 20 28 W |
| Number 7 Ditch | Canal | 105 | Union | 37 27 38 N | 089 22 55 W |
| Number 7 School (historical) | School | 123 | Wayne | 38 26 10 N | 088 13 03 W |
| Number 8 Chapel | Church | 165 | Williamson | 37 48 56 N | 088 48 19 W |
| Number Four Cemetery | Cemetery | 137 | Clay | 38 44 34 N | 088 23 26 W |
| Number Nine School (historical) | School | 136 | Jefferson | 38 15 25 N | 088 42 09 W |
| Number Ten Church | Church | 216 | Vermilion | 40 15 21 N | 087 51 10 W |
| Nunn Cemetery | Cemetery | 138 | Wayne | 38 24 38 N | 088 18 32 W |
| Nuptial School (historical) | School | 162 | Washington | 38 19 00 N | 089 21 58 W |
| Nuttall Middle School | School | 163 | Crawford | 39 01 12 N | 087 44 36 W |
| Nuttle Cemetery | Cemetery | 153 | Crawford | 38 51 56 N | 087 41 55 W |
| Nutwood | Populated Place | 137 | Jersey | 39 05 05 N | 090 33 21 W |
| Nutwood Levee | Levee | | Greene | 39 07 50 N | 090 36 24 W |
| NYA Camp | Locale | 192 | Carroll | 42 09 35 N | 090 10 43 W |
| Nye Chapel United Methodist Church | Church | 139 | Wabash | 38 29 08 N | 087 51 21 W |
| Nye School (historical) | School | 199 | Bureau | 41 14 53 N | 089 25 19 W |
| Nyle Chapel Cemetery | Cemetery | 139 | Wabash | 38 29 08 N | 087 51 21 W |
| Nystrom Lake | Reservoir | 245 | Henry | 41 13 06 N | 090 11 42 W |
| Nystrom Lake Dam | Dam | 245 | Henry | 41 13 06 N | 090 11 42 W |
| O A Thorp Scholastic Academy | School | 189 | Cook | 41 56 57 N | 087 46 41 W |
| O Brien School (historical) | School | 198 | Livingston | 41 02 08 N | 088 22 49 W |
| O John Clark RLA Airport | Airport | 242 | Lake | 42 22 06 N | 087 59 30 W |
| O L Champion Golf Course | Locale | 214 | McDonough | 40 28 57 N | 090 41 16 W |
| O W Huth Middle School | School | 214 | Cook | 41 30 08 N | 087 42 22 W |
| O'Boyle Point | Cape | 224 | Lake | 42 22 35 N | 088 07 54 W |
| O'Brien Cemetery | Cemetery | 232 | Tazewell | 40 33 52 N | 089 32 12 W |
| O'Brien Field | Park | 212 | Coles | 39 28 50 N | 088 10 52 W |
| O'Brien Park | Park | 232 | DuPage | 41 45 39 N | 088 00 55 W |
| O'Brien Run | Stream | | Grundy | 41 20 01 N | 088 30 24 W |
| O'Bryan Cemetery | Cemetery | 207 | Champaign | 39 53 07 N | 088 21 53 W |
| O'Daniel Lodge Lake | Reservoir | 134 | Jefferson | 38 23 42 N | 088 43 54 W |
| O'Daniel Lodge Lake | Reservoir | 130 | Jefferson | 38 23 42 N | 088 43 12 W |
| O'Daniel Lodge Lake Dam Number 1 | Dam | 134 | Jefferson | 38 23 42 N | 088 43 54 W |
| O'Daniel Lodge Lake Dam Number 2 | Dam | 130 | Jefferson | 38 23 42 N | 088 43 12 W |
| O'Donnell Park | Park | 219 | Kane | 41 47 13 N | 088 16 29 W |
| O'Fallon | Populated Place | 167 | St. Clair | 38 35 32 N | 089 54 40 W |
| O'Fallon Assembly of God Church | Church | 167 | St. Clair | 38 35 19 N | 089 54 43 W |
| O'Fallon Cemetery | Cemetery | 163 | St. Clair | 38 35 56 N | 089 54 54 W |
| O'Fallon Central School | School | 167 | St. Clair | 38 35 20 N | 089 56 56 W |
| O'Fallon Christian Church | Church | 167 | St. Clair | 38 35 28 N | 089 54 46 W |
| O'Fallon City Hall | Building | 167 | St. Clair | 38 35 36 N | 089 54 38 W |
| O'Fallon Community Park | Park | 169 | St. Clair | 38 35 12 N | 089 54 25 W |
| O'Fallon High School | School | 166 | St. Clair | 38 35 12 N | 089 54 06 W |
| O'Fallon Post Office | Post Office | 167 | St. Clair | 38 35 25 N | 089 54 37 W |
| O'Fallon United Church of Christ | Church | 165 | St. Clair | 38 35 41 N | 089 54 47 W |
| O'Hair Cemetery | Cemetery | 201 | Edgar | 39 30 46 N | 087 45 16 W |
| O'Hallaren Park | Park | 185 | Cook | 41 44 31 N | 087 40 09 W |
| O'Hara School (historical) | School | 207 | Coles | 39 37 21 N | 088 09 31 W |
| O'Hara Woods Nature Preserve | Park | 202 | Will | 41 38 40 N | 088 06 19 W |
| O'Keefe Elementary School | School | 179 | Cook | 41 46 07 N | 087 34 22 W |
| O'Leary School (historical) | School | 189 | Monroe | 38 14 37 N | 090 07 10 W |
| O'Malley Quadrangle | Park | 189 | Cook | 41 42 27 N | 087 42 47 W |
| O'Malley School (historical) | School | 198 | Grundy | 41 16 04 N | 088 33 28 W |
| O'Neal Cemetery | Cemetery | 198 | Macoupin | 39 26 37 N | 089 58 17 W |
| O'Neal Quarry | Mine | 138 | Hancock | 40 19 06 N | 090 54 49 W |
| O'Neal School (historical) | School | 176 | Sangamon | 39 38 14 N | 089 39 14 W |
| O'Neil Park | Park | 231 | McLean | 40 29 13 N | 089 00 50 W |
| O'Neill Branch | Stream | | La Salle | 41 21 28 N | 088 48 16 W |
| O'Neill Middle School | School | 232 | DuPage | 41 46 47 N | 087 59 58 W |
| O'Neill Quarry | Mine | 232 | Ogle | 41 56 23 N | 089 03 51 W |
| O'Neill School (historical) | School | 244 | Lee | 41 36 01 N | 089 27 26 W |
| O'Rourke School (historical) | School | 256 | McHenry | 42 13 35 N | 088 29 47 W |
| O'Shaughnessy Dining Hall | Building | 209 | Lake | 42 14 02 N | 087 49 45 W |
| O'Toole Elementary School | School | 184 | Cook | 41 46 28 N | 087 40 32 W |
| Oak | Populated Place | 230 | Pope | 37 34 35 N | 088 31 04 W |
| Oak Avenue School | School | 197 | Cook | 41 49 30 N | 087 52 28 W |
| Oak Bank School (historical) | School | 192 | Iroquois | 40 58 54 N | 087 41 36 W |
| Oak Branch | Stream | | Christian | 39 36 26 N | 089 06 03 W |
| Oak Brook | Populated Place | 202 | DuPage | 41 49 58 N | 087 55 44 W |
| Oak Brook Golf Course | Locale | 198 | DuPage | 41 50 40 N | 087 55 58 W |
| Oak Brook Golf Course | Locale | 148 | Madison | 38 50 00 N | 089 50 00 W |
| Oak Brook Polo Club | Locale | 203 | DuPage | 41 50 00 N | 087 56 15 W |
| Oak Chapel School (historical) | School | 181 | Cumberland | 39 15 23 N | 088 11 15 W |
| Oak Creek | Stream | | Henry | 41 25 00 N | 090 05 26 W |
| Oak Creek Shopping Center | Locale | 203 | Cook | 41 36 14 N | 087 45 26 W |
| Oak Crest Cemetery | Cemetery | 225 | DuPage | 41 47 19 N | 088 02 00 W |
| Oak Crest Country Club | Locale | 173 | Sangamon | 39 49 19 N | 089 33 34 W |
| Oak Dale Cemetery | Cemetery | 149 | Jefferson | 38 22 47 N | 088 44 33 W |
| Oak Dale Cemetery | Cemetery | 168 | Washington | 38 15 08 N | 089 32 51 W |
| Oak Dale School (historical) | School | 219 | Mercer | 41 18 37 N | 090 58 14 W |
| Oak Dell School (historical) | School | 216 | Woodford | 40 51 29 N | 089 21 20 W |
| Oak Elementary School | School | 215 | DuPage | 41 47 25 N | 087 55 13 W |
| Oak Forest | Populated Place | 205 | Cook | 41 36 10 N | 087 44 38 W |
| Oak Forest Commons Shopping Center | Locale | 202 | Cook | 41 36 17 N | 087 45 15 W |
| Oak Forest High School | School | 203 | Cook | 41 36 55 N | 087 45 15 W |
| Oak Forest Hospital | Hospital | 203 | Cook | 41 35 54 N | 087 43 57 W |
| Oak Forest School (historical) | School | 183 | Adams | 40 11 02 N | 091 18 11 W |
| Oak Forest School (historical) | School | 213 | Lee | 41 49 30 N | 089 33 48 W |
| Oak Glen Elementary School | School | 190 | Cook | 41 33 51 N | 087 33 58 W |
| Oak Glen Lake | Reservoir | 109 | Massac | 37 11 31 N | 088 46 26 W |
| Oak Glen Nursing Home | Hospital | 223 | Rock Island | 41 24 22 N | 090 28 27 W |
| Oak Glen School (historical) | School | 244 | DeKalb | 42 06 36 N | 088 43 14 W |
| Oak Glen School (historical) | School | 242 | DuPage | 41 58 23 N | 088 11 00 W |
| Oak Glen School (historical) | School | 235 | McHenry | 42 11 19 N | 088 13 41 W |
| Oak Grove | Populated Place | 213 | Lake | 42 17 47 N | 087 55 00 W |
| Oak Grove | Populated Place | 220 | Rock Island | 41 24 38 N | 090 34 14 W |
| Oak Grove (subdivision) | Populated Place | 134 | Cass | 40 01 10 N | 090 24 52 W |
| Oak Grove Baptist Church | Church | 204 | Coles | 39 36 30 N | 088 02 40 W |
| Oak Grove Baptist Church | Church | 156 | Perry | 38 06 59 N | 089 23 25 W |