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 any land owned by such states or a political subdivision of one the states may be acquired only by donation. Interior may enter into cooperative agreements with such states and their political subdivisions, institutions of higher education, nonprofit organizations, Indian tribes, and individuals to (1) identify, interpret, and restore nationally significant historical or cultural and natural resources related to the life of the Mississippi culture within the park, subject to the condition that such an agreement must provide for reasonable public access; and (2) conduct research related to Mississippian culture.