Hat Island is a small island on the eastern edge of the Beaver Island archipelago in Lake Michigan. It is about 10 acres (0.04 km²) in size and located in eastern St. James Township, Charlevoix County, Michigan. It became part of the Michigan Islands National Wildlife Refuge in 1943. During World War 2 it was used as a practice bombing site by the US Navy. Hat Island is roughly four-sided, with an SSE-pointing forepeak that is said to look like the upturned brim of a hat.