Big Oaks National Wildlife Refuge is a 50,000-acre protected area in southeast Indiana near Madison and the largest of the state’s three national wildlife refuges. Established in 2000 on the former Jefferson Proving Ground, it reflects both conservation and a military legacy from the World War II-era munitions testing facility that closed in 1995. Because the U.S. Army used the property for depleted uranium ordnance testing, access requires safety precautions and is limited to about 4,000 acres near Old Timbers Lake. Within that public area, the refuge supports more than 200 bird species and 46 mammal species, while also preserving several sites listed on the National Register of Historic Places.