The Midewin National Tallgrass Prairie (MNTP) is a tallgrass prairie reserve and is preserved as United States National Grassland operated by the United States Forest Service. The first national tallgrass prairie ever designated in the United States and the largest conservation site in the Chicago Wilderness region, it is located on the site of the former Joliet Army Ammunition Plant between the towns of Elwood, Manhattan and Wilmington in northeastern Illinois. Since 2015, it has hosted a conservation herd of American bison to study their interaction with prairie restoration and conservation.