Emmett Till and Mamie Till-Mobley and Roberts Temple National Historic Site Act This bill establishes the Emmett Till and Mamie Till-Mobley and Roberts Temple National Historic Site in Illinois as a unit of the National Park System. The site must not be established until the Department of the Interior enters an agreement with the Roberts Temple providing for public access to, and interpretation, operation, and maintenance of, a site that is sufficient to constitute a manageable park unit. The purpose of the site is to preserve, protect, and interpret (1) the Great Migration, (2) the memorial service and funeral of Emmett Till, (3) the story of the courage and activism of Mamie Till-Mobley that was demonstrated as she transformed the murder of her son into a symbol of racial injustice, and (4) the civil rights movement. Interior may enter into agreements, as appropriate, with public and private entities to provide and facilitate interpretive and educational services, administrative support, and technical assistance relating to the site, within or outside the boundaries of the site. The National Park Service must prepare a general management plan for the site.