| Mifflin Formation | |
|---|---|
| Stratigraphic range: Ordovician | |
_(17203906150).jpg) Fossils from the Mifflin Formation (Lee County, Illinois) | |
| Type | Formation |
| Location | |
| Region |  Illinois  Wisconsin  Iowa |
| Country |  United States |
The Mifflin Formation is a fossil bearing geologic formation in Illinois dating to the Ordovician period.