This article contains a list of fossil-bearing stratigraphic units in the state of Illinois, U.S.
The Black River Group is a geologic group in Illinois and West Virginia. It preserves fossils dating back to the Ordovician period.
The Clore Formation is a geologic formation in Illinois. It preserves fossils dating back to the Carboniferous period.
The Haney Formation is a geologic formation in Illinois. It preserves fossils dating back to the Carboniferous period.
The Kansas City Formation is a geologic formation in Illinois. It preserves fossils dating back to the Carboniferous period.
The Ridenhower Formation is a geologic formation in Illinois. It preserves fossils dating back to the Carboniferous period.
The Grand Tower Limestone is a geologic formation in Illinois. It preserves fossils dating back to the Devonian period.
The St. Laurent Formation is a geologic formation in Illinois. It preserves fossils dating back to the Devonian period.
The Dunleith Formation is a geologic formation in Illinois. It preserves fossils dating back to the Ordovician period.
The Wise Lake Formation is a geologic formation in Illinois. It preserves fossils dating back to the Ordovician period.
The Glenwood Formation is a geologic formation in Illinois. It preserves fossils dating back to the Ordovician period.
The Grand Detour Formation is a geologic formation in Illinois. It preserves fossils dating back to the Ordovician period.
The Neda Formation is a geologic formation in Illinois. It preserves fossils dating back to the Ordovician period.
The Mifflin Formation is a fossil bearing geologic formation in Illinois dating to the Ordovician period.
The Nachusa Formation is a geologic formation in Illinois. It preserves fossils dating back to the Ordovician period.
The Quimbys Mill Formation is a geologic formation in Illinois. It preserves fossils dating back to the Ordovician period.
The Shakopee Formation is a geologic formation in Illinois, Indiana, Wisconsin, and Minnesota. It preserves fossils dating back to the Ordovician period. It is named after the town of Shakopee, Minnesota, where the formation can be seen in bluffs along the Minnesota River
The Clayton Formation is a geologic formation in Illinois. It preserves fossils dating back to the Paleogene period.
The Mosalem Formation is a geologic formation in Illinois. It preserves fossils dating back to the Silurian period.
The Racine Dolomite is a geologic formation in Illinois and Wisconsin. It preserves fossils dating back to the Silurian period.
The Sugar Run Dolomite is a geologic formation in Illinois. It preserves fossils dating back to the Silurian period.
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