Cahokia Mounds Mississippian Culture National Historical Park Act This bill provides for the establishment of the Cahokia Mounds Mississippian Culture National Historical Park in Collinsville, Illinois; Monroe, Madison, and St. Clair Counties, Illinois; and St. Louis City County, Missouri, as a unit of the National Park System. The Department of the Interior may acquire lands and interests within the boundary of the park by donation, purchase, or exchange, except that land owned by such states or their political subdivisions may only be acquired by donation. Interior may enter into cooperative agreements with such states and their political subdivisions, colleges and universities, nonprofit organizations, Indian tribes, and individuals to (1) mark, interpret, and restore nationally significant historic or cultural and natural resources related to the life of the Mississippi culture within the park, if the agreement provides for reasonable public access; and (2) conduct research related to Mississippi culture.