St. Louis Limestone.
Lower Pope Group (Aux Vases Sandstone through Glen Dean Limestone).
Warsaw Formation and Salem Limestone in western Illinois.
Kimmswick (Trenton) Limestone and Decorah Formation in southern and western Illinois.
Meppen Limestone, Fern Glen Formation, and Burlington-Keokuk Limestone.
Ste. Genevieve Limestone.
Platteville Group, includes Pecatonica, Mifflin, Grand Detour, Nachusa, and Quimbys Mill Formations; includes Plattin Limestone in southwestern Illinois.
Maquoketa Formation or Group, includes Cape Limestone, Cape La Croix Shale, Thebes Sandstone, Orchard Creek Shale, Girardeau Limestone, and Leemon Formation in southern Illinois; includes Scales Shale, Fort Atkinson Limestone, Brainard Shale, and Neda Formation in northern Illinois; includes Noix Oolite in western Illinois.
Ancell Group, includes St. Peter Sandstone, Dutchtown Limestone, Joachim Dolomite, and Glenwood Formation; includes Prairie du Chien Group in Jo Daviess County of northwestern Illinois.
Alluvium - clay, silt, sand, and gravel.