Feature Name | Class | Elev. meters | County | Latitude DMS | Longitude DMS |
| Twin Culvert Cave Nature Preserve | Park | 170 | Pike | 39 26 45 N | 090 39 50 W |
| Twin Echo Elementary School | School | 144 | Madison | 38 39 01 N | 089 59 46 W |
| Twin Faun Lake | Reservoir | 164 | Bureau | 41 17 18 N | 089 30 30 W |
| Twin Gardens Airport | Airport | 271 | Henry | 42 24 30 N | 088 39 10 W |
| Twin Grove | Populated Place | 250 | McLean | 40 29 36 N | 089 04 47 W |
| Twin Grove | Woods | 247 | Lee | 41 46 17 N | 089 02 05 W |
| Twin Grove Baptist Church | Church | 217 | Lake | 42 10 04 N | 087 59 08 W |
| Twin Grove Cemetery | Cemetery | 250 | Lee | 41 45 40 N | 089 01 45 W |
| Twin Grove Junior High School | School | 218 | Lake | 42 10 03 N | 087 58 54 W |
| Twin Groves Park | Park | 216 | Lake | 42 09 58 N | 087 58 52 W |
| Twin Islands | Island | 130 | Greene | 39 22 58 N | 090 37 11 W |
| Twin Lake | Lake | 142 | Adams | 39 51 55 N | 091 24 56 W |
| Twin Lakes | Lake | 122 | Clinton | 38 28 45 N | 089 33 01 W |
| Twin Lakes | Lake | 255 | Cook | 42 08 55 N | 088 10 37 W |
| Twin Lakes | Lake | 234 | Lake | 42 20 33 N | 087 58 53 W |
| Twin Lakes | Lake | 195 | Monroe | 38 17 41 N | 090 11 37 W |
| Twin Lakes | Lake | 136 | Pike | 39 28 13 N | 090 58 47 W |
| Twin Lakes | Locale | 164 | Henderson | 40 51 23 N | 090 58 45 W |
| Twin Lakes | Reservoir | 201 | Edgar | 39 37 48 N | 087 40 35 W |
| Twin Lakes | Reservoir | 149 | Madison | 38 43 42 N | 089 51 54 W |
| Twin Lakes Dam | Dam | 149 | Madison | 38 43 42 N | 089 51 54 W |
| Twin Lakes Golf Course | Locale | 222 | DuPage | 41 46 58 N | 087 59 10 W |
| Twin Lakes Park | Park | 222 | DuPage | 41 46 54 N | 087 58 54 W |
| Twin Lakes Recreational Area | Park | 216 | Cook | 42 06 16 N | 088 00 51 W |
| Twin Oaks Baptist Church | Church | 270 | Kane | 42 05 26 N | 088 20 04 W |
| Twin Oaks Country Club | Locale | 219 | McDonough | 40 33 19 N | 090 52 48 W |
| Twin Oaks Missionary Baptist Church | Church | 215 | Tazewell | 40 38 27 N | 089 30 01 W |
| Twin Oaks Picnic Area | Locale | 146 | Hamilton | 38 03 40 N | 088 23 39 W |
| Twin Oaks Place Shopping Center | Locale | 185 | Will | 41 31 21 N | 088 09 31 W |
| Twin Orchard Country Club | Locale | 229 | Lake | 42 11 13 N | 087 59 51 W |
| Twin Orchard Country Club (historical) | Locale | 200 | Cook | 41 58 33 N | 087 54 07 W |
| Twin Ponds | Lake | 129 | Cass | 39 53 01 N | 090 34 19 W |
| Twin Ponds (historical) | Lake | 134 | Calhoun | 39 22 35 N | 090 50 28 W |
| Twin Ponds Golf Course | Locale | 267 | McHenry | 42 13 25 N | 088 17 04 W |
| Twin Rivers District Public Library | Building | 179 | Henry | 41 28 08 N | 090 21 29 W |
| Twin Sister Hills Park | Park | 228 | Winnebago | 42 15 40 N | 089 02 59 W |
| Twin Springs | Spring | 132 | Jersey | 38 58 42 N | 090 32 44 W |
| Twinbrook Elementary School | School | 231 | Cook | 42 02 47 N | 088 04 08 W |
| Twing Memorial Baptist Church | Church | 187 | Madison | 38 54 09 N | 090 11 33 W |
| Twining Cemetery | Cemetery | 223 | Will | 41 26 23 N | 087 52 18 W |
| Twiss Hill School (historical) | School | 169 | St. Clair | 38 33 12 N | 090 04 47 W |
| Twitchell Cemetery | Cemetery | 133 | Hardin | 37 27 49 N | 088 22 55 W |
| Twitchell Mine | Mine | 129 | Hardin | 37 27 57 N | 088 22 48 W |
| Two Branch Hollow | Valley | | Calhoun | 38 53 07 N | 090 36 37 W |
| Two First National Building | Building | 181 | Cook | 41 52 53 N | 087 37 52 W |
| Two Hundred Arlington Place Shopping Center | Locale | 212 | Cook | 42 05 03 N | 087 58 52 W |
| Two Hundred Eight South LaSalle Building | Building | 181 | Cook | 41 52 45 N | 087 37 57 W |
| Two Illinois Center | Building | 177 | Cook | 41 53 14 N | 087 37 22 W |
| Two Mile Grove Cemetery | Cemetery | 184 | Logan | 39 56 16 N | 089 10 26 W |
| Two Prudential Plaza | Building | 178 | Cook | 41 53 07 N | 087 37 22 W |
| Two Rivers Camp | Locale | 213 | Brown | 39 52 41 N | 090 52 00 W |
| Two Rivers Marina | Locale | 140 | Pike | 39 27 40 N | 091 02 28 W |
| Two Story Hill | Summit | 188 | Calhoun | 38 53 16 N | 090 33 40 W |
| Twomile Branch | Stream | | Moultrie | 39 36 26 N | 088 32 44 W |
| Twomile Creek | Stream | | Jefferson | 38 19 13 N | 088 50 50 W |
| Twomile Creek | Stream | | Pike | 39 29 32 N | 090 57 50 W |
| Twomile Island | Island | 158 | Henderson | 40 44 08 N | 091 05 20 W |
| Twomile School (historical) | School | 198 | Moultrie | 39 37 34 N | 088 33 58 W |
| Twomile Slough | Stream | | Champaign | 39 52 51 N | 088 22 40 W |
| Ty Warner Park | Park | 224 | DuPage | 41 48 53 N | 087 58 15 W |
| Tygett School (historical) | School | 171 | Union | 37 31 52 N | 089 09 52 W |
| Tyler Cemetery | Cemetery | 137 | Wayne | 38 24 12 N | 088 39 22 W |
| Tyler Creek | Stream | | Kane | 42 03 27 N | 088 17 15 W |
| Tyler Creek Forest Preserve | Park | 237 | Kane | 42 03 51 N | 088 17 48 W |
| Tyler Creek Plaza Shopping Center | Locale | 248 | Kane | 42 03 33 N | 088 18 47 W |
| Tyler Elementary School | School | 258 | DeKalb | 41 55 11 N | 088 45 57 W |
| Tyler Post Office (historical) | Post Office | 252 | Winnebago | 42 22 32 N | 089 19 50 W |
| Tyler School (historical) | School | 190 | Will | 41 38 18 N | 088 09 43 W |
| Tylerville School (historical) | School | 221 | Warren | 40 59 18 N | 090 29 48 W |
| Tyng Primary School | School | 163 | Peoria | 40 40 45 N | 089 37 42 W |
| Tyrell School (historical) | School | 273 | Kane | 42 05 34 N | 088 21 33 W |
| Tyson Creek | Stream | | Hancock | 40 36 58 N | 091 18 20 W |
| U Lake | Reservoir | 224 | Knox | 40 59 12 N | 090 05 11 W |
| U S Cellular Field | Park | 181 | Cook | 41 49 48 N | 087 38 02 W |
| U S Grant Middle School | School | 180 | Sangamon | 39 47 57 N | 089 41 00 W |
| Udall Park | Park | 212 | Cook | 42 01 09 N | 087 58 31 W |
| Udina | Populated Place | 275 | Kane | 42 02 36 N | 088 22 34 W |
| Udina Cemetery | Cemetery | 274 | Kane | 42 02 35 N | 088 22 39 W |
| Ukrainian Autocepholous Orthodox Cathedral | Church | 182 | Cook | 41 53 51 N | 087 41 40 W |
| Ukrainian Baptist Church | Church | 182 | Cook | 41 54 03 N | 087 40 39 W |
| Ukrainian Baptist Church | Church | 188 | Cook | 41 50 57 N | 087 47 35 W |
| Ukrainian Christian Pentecostal Church | Church | 183 | Cook | 41 54 01 N | 087 42 01 W |
| Ukrainian Culture Center of Saint Volovymy and Olha Parish | Building | 183 | Cook | 41 53 44 N | 087 41 03 W |
| Ulah | Populated Place | 221 | Henry | 41 16 09 N | 090 08 46 W |
| Ullin | Populated Place | 104 | Pulaski | 37 16 37 N | 089 11 00 W |
| Ullin City Cemetery | Cemetery | 102 | Pulaski | 37 16 18 N | 089 11 38 W |
| Ullin Election Precinct | Civil | 100 | Pulaski | 37 16 01 N | 089 11 09 W |
| Ullrich | Populated Place | 206 | Moultrie | 39 44 27 N | 088 40 53 W |
| Ullrich School | School | 206 | Macon | 39 51 08 N | 088 57 00 W |
| Ulrich Lake | Reservoir | 115 | Pulaski | 37 15 06 N | 089 00 18 W |
| Ulrich Lake Dam | Dam | 115 | Pulaski | 37 15 06 N | 089 00 18 W |
| Umc Trauma Center Heliport | Airport | 212 | Rock Island | 41 30 10 N | 090 31 35 W |
| Uncle Chucks Airport | Airport | 267 | DeKalb | 41 55 04 N | 088 47 21 W |
| Undercliff | Populated Place | 139 | Putnam | 41 11 16 N | 089 21 58 W |
| Underwood Cemetery | Cemetery | 162 | Jackson | 37 56 18 N | 089 27 56 W |
| Underwood Pond | Reservoir | 209 | Peoria | 40 53 12 N | 089 47 24 W |
| Underwood Pond Dam | Dam | 209 | Peoria | 40 53 12 N | 089 47 24 W |
| Unification Church | Church | 182 | Cook | 42 01 05 N | 087 39 58 W |
| Uninty Cemetery | Cemetery | 98 | Alexander | 37 09 45 N | 089 16 23 W |
| Union | Populated Place | 220 | Logan | 40 17 15 N | 089 22 01 W |
| Union | Populated Place | 154 | Mason | 40 23 27 N | 089 48 34 W |
| Union | Populated Place | 256 | McHenry | 42 13 59 N | 088 32 32 W |
| Union | Populated Place | 193 | Will | 41 29 49 N | 088 01 24 W |
| Union Avenue Christian Church | Church | 209 | Montgomery | 39 10 40 N | 089 39 04 W |
| Union Avenue United Methodist Church | Church | 182 | Cook | 41 48 52 N | 087 38 37 W |
| Union Baptist Church | Church | 184 | Adams | 39 56 35 N | 091 24 01 W |
| Union Baptist Church | Church | 137 | Cass | 40 01 04 N | 090 25 08 W |
| Union Baptist Church | Church | 184 | Cook | 41 38 22 N | 087 42 03 W |
| Union Baptist Church | Church | 161 | Madison | 38 53 39 N | 090 10 51 W |
| Union Baptist Church | Church | 125 | St. Clair | 38 39 26 N | 090 09 47 W |