# List of fossiliferous stratigraphic units in Illinois

This article contains a list of fossil-bearing stratigraphic units in the state of Illinois, U.S.

## Sites

| Group or Formation | Period |
| Altamont Formation | Carboniferous |
| Platteville Limestone | Ordovician |
| St. Louis Limestone | Carboniferous |
| Brainard Formation | Ordovician |
| Carbondale Formation | Carboniferous |
| Caseyville Formation | Carboniferous |
| Cedar Valley Formation | Devonian |
| Little Cedar Formation | Devonian |
| Chester Formation | Carboniferous |
| Hardinsburg Formation | Carboniferous |
| Clore Formation | Carboniferous |
| Tar Springs Formation | Carboniferous |
| Chouteau Formation | Carboniferous |
| Clayton Formation | Paleogene |
| Decorah Shale | Ordovician |
| Degonia Formation | Carboniferous |
| Des Moines Formation | Carboniferous |
| Drurey Shale | Carboniferous |
| English River Formation | Carboniferous |
| Fort Scott Limestone | Carboniferous |
| Fraileys Formation | Carboniferous |
| Fraileys Shale | Carboniferous |
| Galena Dolomite | Ordovician |
| Dubuque Formation | Ordovician |
| Dunleith Formation | Ordovician |
| Guttenberg Formation | Ordovician |
| Ion Formation | Ordovician |
| Wise Lake Formation | Ordovician |
| Glen Park Formation | Carboniferous |
| Glenwood Formation | Ordovician |
| Golconda Formation | Carboniferous |
| Golconda Group | Carboniferous |
| Haney Formation | Carboniferous |
| Gower Formation | Silurian |
| Grand Detour Formation | Ordovician |
| Grand Tower Limestone | Devonian |
| Haney Limestone | Carboniferous |
| Iola Formation | Carboniferous |
| Kansas City Formation | Carboniferous |
| Keokuk Limestone | Carboniferous |
| Spoon Formation | Carboniferous |
| Kimmswick Limestone | Ordovician |
| Kinkaid Formation | Carboniferous |
| Linton Formation | Carboniferous |
| Maquoketa Formation | Ordovician |
| Brainard Shale | Ordovician |
| Fort Atkinson Limestone | Ordovician |
| Neda Formation | Ordovician |
| Scales Shale | Ordovician |
| Mattoon Formation | Carboniferous |
| McCraney Limestone | Carboniferous |
| Bond Formation | Carboniferous |
| Patoka Formation | Carboniferous |
| Shelburn Formation | Carboniferous |
| McLeansbough Formation | Carboniferous |
| Mifflin Formation | Ordovician |
| Mosalem Formation | Silurian |
| Nachusa Formation | Ordovician |
| Glen Dean Formation | Carboniferous |
| Orchard Creek Shale | Ordovician |
| Paint Creek Formation | Carboniferous |
| Pawnee Formation | Carboniferous |
| Pecatonica Formation | Ordovician |
| McGregor Formation | Ordovician |
| Prosser Limestone | Ordovician |
| Purington Shale | Carboniferous |
| Quimbys Mill Formation | Ordovician |
| Racine Dolomite | Silurian |
| Ridenhower Formation | Carboniferous |
| Salem Formation | Carboniferous |
| Shakopee Formation | Ordovician |
| Spechts Ferry Formation | Ordovician |
| St. Laurent Formation | Devonian |
| St. Louis Formation | Carboniferous |
| St. Peter Sandstone | Ordovician |
| Ste. Genevieve Limestone | Carboniferous |
| Sturgis Formation | Carboniferous |
| Sugar Run Dolomite | Silurian |
| Tradewater Formation | Carboniferous |
| Verdigris Formation | Carboniferous |
| Waltersburg Formation | Carboniferous |
| Warsaw Formation | Carboniferous |
| Wilhelmi Formation | Silurian |