The St. Louis Limestone is a large geologic formation covering a wide area of the midwest of the United States. It is named after an exposure at St. Louis, Missouri. It consists of sedimentary limestone with scattered chert beds, including the heavily chertified Lost River Chert Bed in the Horse Cave Member. It is exposed at the surface through western Kentucky and Middle Tennessee, including the city of Clarksville, Tennessee. The limestone deposit is Mississippian in age, in the Meramecian series, roughly 330-340 million years old.

St. Louis Limestone
Stratigraphic range: Mississippian Sub-period
Rock anhydrite (St. Louis Limestone; subsurface gypsum mine in Martin County, Indiana)
Type	Geological formation
Unit of	Blue River Group
Sub-units	Dover Chert, Horse Cave Member, Sisson Member
Underlies	Ste. Genevieve Limestone
Overlies	Salem Formation[1]
Thickness	up to 100 feet (30 m)[2]
Lithology
Primary	Limestone
Other	Shale, chert[2]
Location
Region	Illinois, Indiana, Tennessee, Kentucky and Missouri
Country	United States
Type section
Named for	St. Louis, Missouri[1]
Named by	Englemann
Year defined	1847

Fossils commonly found in the St. Louis include the rugosan corals Lithostrotion and Lithostrotionella and the bryozoan Fenestrellina.