Minuteman Missile National Historic Site Boundary Modification Act - Amends the Minuteman Missile National Historic Site Establishment Act of 1999 to modify the boundary of the Minuteman Missile National Historic Site in South Dakota by including in the Historic Site the following lands and interests in Jackson County, South Dakota, identified on the map entitled "Minuteman Missile National Historic Site Boundary Modification," and dated July 17, 2009: (1) approximately 25 acres of land north of exit 131 on Interstate 90 in Jackson County for the construction and use of a visitor facility and administrative site; and (2) approximately 3.65 acres of land at the Delta 1 Launch Control Facility for the construction and use of a parking lot and for other administrative purposes.
Directs the Secretary of Agriculture (USDA) to transfer the administrative jurisdiction over such lands to the Secretary of the Interior and modify the boundaries of the Buffalo Gap National Boundary Grassland to exclude such land.