The Milwaukee Formation is a fossil-bearing geological formation of Middle Devonian age in Milwaukee County, Wisconsin. It stands out for the exceptional diversity of its fossil biota. Included are many kinds of marine protists, invertebrates, and fishes, as well as early trees and giant fungi. Once a prolific source of fossils, the Milwaukee Formation exposures are now mostly buried, inaccessible, on private property, or located in areas where collecting is prohibited. Most of these exposures are or were located along the Milwaukee River and Lake Michigan shore.