In Illinois, caves can be found in four distinct karst regions. All those regions are located along the western border to Iowa and Missouri, which is formed by the Mississippi river..
Most caves are located in Mississippian limestones. During the Mississippian Period much of Illinois was covered by a shallow sea. In this oxygene rich and warm sea carbonatic sediments, limestone and dolomite were deposited. Until now several hundred caves are known, but there are no show caves in the whole state. Three of the caves may be visited on easy cave trekking tours, and there is one, which we classified as a show cave as we lack a better category. It is developed with trails and electric light, but it is used for concerts, reunions and wedding receptions.
In a few caves in Monroe and St. Clair counties, the Illinois cave amphipod lives, an endemic small shrimp-like creature, that exists nowhere else in the world. They inhabit the bottoms of pools and riffles in large cave streams, feeding on decaying leaf litter and organic debris. But the urbanization of the greater St. Louis metropolitan area, without appropriate sewage treatment and disposal, is threatening to the survival of those amphipods. Other serious threats are siltation and the presence of agricultural chemicals in subterranean aquifers.
There also was a single show mine, in the Galena lead mining district, which has unfortunately been closed a few years ago.