Fort Donelson National Battlefield Act of 2004 - (Sec. 2) Declares that the Fort Donelson National Battlefield exists as a unit of the National Park System (the System) to commemorate the Battle of Fort Donelson in February 1862 and the campaign conducted by General Ulysses S. Grant and Admiral Andrew H. Foote that resulted in the capture of the Fort by Union forces.
Revises the boundary of the Fort Donelson Battlefield to include the site of Fort Donelson and associated land that has been acquired by the Secretary of the Interior for administration by the National Park Service, including Fort Donelson National Cemetery, in Stewart County, Tennessee, and the site of Fort Heiman and associated land in Calloway County, Kentucky. Includes in the Battlefield any land acquired pursuant to this Act.
(Sec. 3) Authorizes the Secretary of the Interior to acquire only by purchase from willing sellers, by donation, or by exchange with willing owners for inclusion in the Fort Donelson National Battlefield land, interests, and improvements: (1) within the boundaries of the Battlefield; and (2) outside such boundaries if the land has been identified by the American Battlefield Protection Program as part of the battlefield associated with Fort Donelson or the Secretary otherwise determines that acquisition will protect critical resources associated with the Battle of Fort Donelson in 1862 and the Union campaign that resulted in the capture of the Fort. Requires the Secretary, upon acquisition of such land or interests, to revise the boundaries of the Battlefield to include the acquired property. Limits the total area encompassed by the Battlefield to 2,000 acres.
(Sec. 4) Requires the Secretary to administer the Fort Donelson National Battlefield in accordance with this Act and the laws generally applicable to units of the System, including the National Park Service Organic Act and the Historic Sites, Buildings, and Antiquities Act.
(Sec. 5) Directs the Secretary and the Secretary of Agriculture to enter into a memorandum of understanding to facilitate cooperative protection and interpretation of the remaining vestiges of Fort Henry and other existing Civil War resources affiliated with the Fort Donelson campaign and located in the Land Between the Lakes National Recreation Area.
(Sec 6) Repeals specified provisions of law concerning Fort Donelson National Battlefield.