Shiloh National Military Park Boundary Adjustment and Parker's Crossroads Battlefield Designation Act This bill modifies the boundary of Shiloh National Military Park in Tennessee and Mississippi to include the following areas: (1) Fallen Timbers Battlefield, (2) Russell House Battlefield, and (3) Davis Bridge Battlefield. The Department of the Interior may acquire these lands by donation, exchange, or purchase from willing sellers. The Parker's Crossroads Battlefield in Tennessee is established as an affiliated area of the National Park System.