Feature Name | Class | Elev. meters | County | Latitude DMS | Longitude DMS |
| Clark School (historical) | School | 169 | Fulton | 40 24 15 N | 090 03 31 W |
| Clark School (historical) | School | 204 | Iroquois | 40 48 23 N | 087 33 29 W |
| Clark School (historical) | School | 164 | Jasper | 39 05 55 N | 088 02 04 W |
| Clark School (historical) | School | 162 | Lawrence | 38 42 05 N | 087 49 26 W |
| Clark School (historical) | School | 196 | Schuyler | 40 06 21 N | 090 48 38 W |
| Clark School (historical) | School | 229 | Vermilion | 40 24 53 N | 087 49 04 W |
| Clark Square Park | Park | 175 | Cook | 42 01 59 N | 087 40 09 W |
| Clarkdale (subdivision) | Populated Place | 189 | Cook | 41 44 34 N | 087 42 58 W |
| Clarke City | Populated Place | 180 | Kankakee | 41 09 29 N | 088 14 34 W |
| Clarke Heliport | Airport | 244 | DuPage | 41 59 11 N | 088 06 04 W |
| Clarke Point Shoal | Bar | 175 | Cook | 41 45 26 N | 087 32 05 W |
| Clarke School (historical) | School | 270 | DeKalb | 42 00 04 N | 088 47 47 W |
| Clarks Island | Island | 149 | La Salle | 41 19 07 N | 088 41 30 W |
| Clarks Mound | Summit | 196 | St. Clair | 38 34 45 N | 090 04 14 W |
| Clarks Point | Cape | 179 | Cook | 41 45 24 N | 087 32 48 W |
| Clarksburg | Populated Place | 189 | Shelby | 39 19 48 N | 088 44 30 W |
| Clarksburg IL | Populated Place | 186 | Shelby | 39 19 05 N | 088 45 52 W |
| Clarksburg Townhall | Building | 189 | Shelby | 39 19 54 N | 088 44 58 W |
| Clarksdale | Populated Place | 190 | Christian | 39 29 23 N | 089 22 04 W |
| Clarkson Park | Park | 191 | Cook | 42 06 03 N | 087 46 33 W |
| Clarksville | Populated Place | 201 | Clark | 39 27 06 N | 087 47 52 W |
| Clarksville | Populated Place | 229 | McLean | 40 39 02 N | 088 50 54 W |
| Clarksville Baptist Cemetery | Cemetery | 198 | Clark | 39 26 52 N | 087 47 38 W |
| Clarksville Cemetery | Cemetery | 227 | McLean | 40 39 18 N | 088 51 04 W |
| Clarksville Island | Island | 136 | Calhoun | 39 22 10 N | 090 52 57 W |
| Clarmin | Populated Place | 153 | Washington | 38 13 16 N | 089 41 58 W |
| Clarmin School (historical) | School | 153 | Washington | 38 13 18 N | 089 41 57 W |
| Clary Creek | Stream | | Cass | 40 06 15 N | 090 01 10 W |
| Clary Spring | Spring | 150 | Jersey | 39 01 46 N | 090 31 52 W |
| Classen Field RLA Airport | Airport | 198 | Iroquois | 40 49 00 N | 087 59 30 W |
| Classen School (historical) | School | 201 | Iroquois | 40 50 18 N | 088 01 57 W |
| Classics Building | Building | 180 | Cook | 41 47 16 N | 087 36 03 W |
| Classon School (historical) | School | 184 | La Salle | 41 26 47 N | 088 43 36 W |
| Claude W Foss Memorial Home (historical) | Building | 181 | Rock Island | 41 30 18 N | 090 32 49 W |
| Claus | Populated Place | 227 | Will | 41 22 11 N | 087 36 36 W |
| Claus Farm Recreation Area | Park | 246 | DuPage | 41 58 25 N | 088 05 34 W |
| Clavery Park | Park | 204 | Lake | 42 10 15 N | 087 52 22 W |
| Clay Bank | Cliff | 159 | Schuyler | 40 11 30 N | 090 45 08 W |
| Clay Cemetery | Cemetery | 300 | Jo Daviess | 42 15 11 N | 089 55 18 W |
| Clay Cemetery | Cemetery | 230 | Knox | 40 55 05 N | 090 26 23 W |
| Clay City | Populated Place | 132 | Clay | 38 41 19 N | 088 21 15 W |
| Clay City Cemetery | Cemetery | 146 | Clay | 38 40 34 N | 088 20 58 W |
| Clay City Christian Church | Church | 137 | Clay | 38 40 54 N | 088 21 13 W |
| Clay City Church of God | Church | 131 | Clay | 38 41 27 N | 088 21 26 W |
| Clay City Elementary School | School | 133 | Clay | 38 41 11 N | 088 21 18 W |
| Clay City First Baptist Church | Church | 133 | Clay | 38 41 13 N | 088 21 18 W |
| Clay City High School | School | 134 | Clay | 38 41 01 N | 088 21 07 W |
| Clay City Oil Field | Oilfield | 131 | Wayne | 38 20 27 N | 088 20 39 W |
| Clay City Oil Field | Oilfield | 144 | Wayne | 38 34 14 N | 088 18 34 W |
| Clay City United Methodist Church | Church | 133 | Clay | 38 41 13 N | 088 21 16 W |
| Clay City West Oil Field | Oilfield | 134 | Clay | 38 37 41 N | 088 25 20 W |
| Clay County | Civil | 153 | Clay | 38 50 00 N | 088 29 00 W |
| Clay County Courthouse | Building | 147 | Clay | 38 46 20 N | 088 30 06 W |
| Clay County Hospital | Hospital | 148 | Clay | 38 40 32 N | 088 29 00 W |
| Clay County Hospital Heliport | Airport | 148 | Clay | 38 40 31 N | 088 29 00 W |
| Clay Elementary School | School | 178 | Cook | 41 39 16 N | 087 32 38 W |
| Clay Hill School (historical) | School | 173 | Jefferson | 38 27 38 N | 089 07 35 W |
| Clay Lick Creek | Stream | | Jackson | 37 36 36 N | 089 15 15 W |
| Clay School | School | 171 | Madison | 38 40 40 N | 089 56 42 W |
| Clay School (historical) | School | 312 | Jo Daviess | 42 15 17 N | 089 55 50 W |
| Clay School (historical) | School | 229 | Knox | 40 55 09 N | 090 25 21 W |
| Clay Street Elementary School | School | 274 | McHenry | 42 19 16 N | 088 26 45 W |
| Claybough Cemetery | Cemetery | 203 | McDonough | 40 19 07 N | 090 36 50 W |
| Claybourn Gospel Church | Church | 180 | Cook | 41 54 19 N | 087 38 29 W |
| Clayburg School (historical) | School | 213 | Fulton | 40 30 33 N | 090 09 43 W |
| Claypool | Populated Place | 155 | Grundy | 41 20 45 N | 088 23 14 W |
| Claypool Ditch | Canal | 165 | Grundy | 41 18 08 N | 088 17 38 W |
| Claypool School (historical) | School | 179 | Grundy | 41 18 23 N | 088 26 58 W |
| Claypool Woods | Populated Place | 155 | Grundy | 41 20 39 N | 088 24 00 W |
| Clays Prairie | Populated Place | 186 | Edgar | 39 41 13 N | 087 33 48 W |
| Clays Prairie School (historical) | School | 193 | Edgar | 39 40 55 N | 087 33 45 W |
| Claysville | Populated Place | 186 | Sangamon | 39 52 02 N | 089 54 01 W |
| Clayton | Populated Place | 223 | Adams | 40 01 53 N | 090 57 38 W |
| Clayton Andrews County Forest Preserve | Reserve | 244 | Winnebago | 42 26 33 N | 088 57 24 W |
| Clayton Cemetery | Cemetery | 131 | Franklin | 37 52 39 N | 088 55 21 W |
| Clayton Cemetery | Cemetery | 228 | Woodford | 40 50 16 N | 089 05 08 W |
| Clayton Christian Church | Church | 223 | Adams | 40 01 53 N | 090 57 24 W |
| Clayton Hollow | Valley | | Gallatin | 37 37 51 N | 088 17 12 W |
| Clayton Reservoir Dam | Dam | 209 | Adams | 40 00 42 N | 090 57 07 W |
| Clayton Run | Stream | | La Salle | 41 19 12 N | 089 01 44 W |
| Clayton School (historical) | School | 226 | Ford | 40 57 06 N | 088 11 20 W |
| Clayton Township Cemetery | Cemetery | 231 | Woodford | 40 51 14 N | 089 07 51 W |
| Claytonville | Populated Place | 201 | Iroquois | 40 34 01 N | 087 49 23 W |
| Claytonville Post Office | Post Office | 201 | Iroquois | 40 33 58 N | 087 49 20 W |
| Claywell Cemetery | Cemetery | 164 | Scott | 39 36 10 N | 090 28 49 W |
| Claywell School (historical) | School | 160 | Scott | 39 36 08 N | 090 28 38 W |
| Clear Creek | Stream | | Alexander | 37 16 37 N | 089 25 18 W |
| Clear Creek | Stream | | Cass | 39 54 19 N | 090 27 14 W |
| Clear Creek | Stream | | Christian | 39 38 53 N | 089 28 33 W |
| Clear Creek | Stream | | Christian | 39 39 40 N | 089 28 41 W |
| Clear Creek | Stream | | Cumberland | 39 20 06 N | 088 09 09 W |
| Clear Creek | Stream | | Cumberland | 39 21 30 N | 088 18 38 W |
| Clear Creek | Stream | | Cumberland | 39 22 22 N | 088 27 47 W |
| Clear Creek | Stream | | Edgar | 39 26 45 N | 087 30 01 W |
| Clear Creek | Stream | | Jo Daviess | 42 26 48 N | 090 02 53 W |
| Clear Creek | Stream | | Kendall | 41 34 09 N | 088 35 45 W |
| Clear Creek | Stream | | Logan | 40 14 09 N | 089 10 16 W |
| Clear Creek | Stream | | Ogle | 41 55 25 N | 089 23 16 W |
| Clear Creek | Stream | | Putnam | 41 08 21 N | 089 19 27 W |
| Clear Creek | Stream | | Sangamon | 39 47 28 N | 089 29 32 W |
| Clear Creek Ditch | Canal | 101 | Union | 37 23 30 N | 089 21 11 W |
| Clear Creek School (historical) | School | 177 | Cumberland | 39 20 47 N | 088 09 42 W |
| Clear Lake | Lake | 134 | Cass | 40 03 08 N | 090 18 30 W |
| Clear Lake | Lake | 221 | Champaign | 40 06 55 N | 088 17 21 W |
| Clear Lake | Lake | 124 | Clinton | 38 28 49 N | 089 30 57 W |
| Clear Lake | Lake | 155 | Henderson | 40 43 23 N | 091 05 03 W |
| Clear Lake | Lake | 133 | Mason | 40 25 35 N | 089 55 35 W |
| Clear Lake | Lake | 130 | Perry | 38 02 03 N | 089 24 02 W |
| Clear Lake | Lake | 140 | Pike | 39 43 46 N | 091 21 30 W |
| Clear Lake | Lake | 157 | Sangamon | 39 49 15 N | 089 32 02 W |