Mifflin Formation

{{Infobox rockunit

| name = Mifflin Formation

| image = Amplexograptus maxwelli fossil graptolites (Mifflin Formation, Ordovician; Lee County, Illinois, USA) (17203906150).jpg

| caption = Fossils from the Mifflin Formation (Lee County, Illinois)

| type = Formation

| age = Ordovician

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| region = Illinois, Wisconsin, Iowa

| country = United States

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The Mifflin Formation is a fossil bearing geologic formation in Illinois dating to the Ordovician period.