Fort Knox ( Maine ) Fort Knox , now Fort Knox State Park or Fort Knox State Historic Site , in Maine was built from 1844 - 1869 . It is located on the western bank of the Penobscot River in the town of Prospect , Maine , about from the mouth of the river . It was the first fort in Maine built of granite ( instead of wood ) . It is named after Henry Knox , the first US Secretary of War , who at the end of his life lived not far away in Thomaston , Maine . The fort was designated a National Historic Landmark in 1970 . Construction began during a period of tension between the United Kingdom and the United States over issues about the Canadian border following the Aroostook War . The intent was to defend the Penobscot River and Bangor , Maine , a major source of shipbuilding lumber . Construction funding from Congress was intermittent , and the fort ' s design was never fully completed although nearly a million dollars were spent . Granite was quarried five miles ( 8 km ) upriver from Mount Waldo in Frankfort , Maine . It had two batteries facing the river , each equipped with a hot shot furnace to heat cannon shots hot enough to set ships on fire . These became obsolete with the changeover from wooden ships to ironclads . The fort was manned during the U . S . Civil War by volunteers from Maine ( mostly recruits in training before assignment to active duty ) . At this time the bulk of the work on the fort , including adapting the batteries to use the recently invented Rodman cannon was finished under the supervision of Thomas Lincoln Casey . It was manned during the Spanish - American War by a regiment from Connecticut . The garrison was reduced to one upon their departure at the end of the war . The fort never saw battle . In 1923 , the federal government declared the fort excess property and put its grounds up for sale . It was bought by the state of Maine for $ 2 , 121 . It is now a Maine state historic site and was declared a U . S . National Historic Landmark on December 30 , 1970 . Fort Knox also serves as the entry site for the Observation Tower of the Penobscot Narrows Bridge , which opened to the public on May 19 , 2007 . The Friends of Fort Knox , a nonprofit group formed in the 1990s , has been responsible for many fort repairs and improvements . Friends of Fort Knox projects include the transformation of the Torpedo Storage Shed into the Visitor and Education Center , restoration of the Officer ' s Quarters , installation of interpretive panels , repair of Battery A powder magazine , restoration and display of four 24 - pound flank defense howitzer s , repair and opening of the enlisted men ' s quarters cistern rooms and extensive masonry repair . The Friends reached an agreement with the State Department of Conservation to take over day - to - day operations of the Fort , and began doing so on April 15 , 2012 . The State retains ownership of the fort as part of the agreement . The lease runs through 2015 and requires the Friends to be responsible for all maintenance of the grounds as well as the interior and exterior of buildings on the property . The Friends may also improve or alter the fort as long as any changes are consistent with the law . After 2012 the Friends can set the entrance fee to the fort , with the approval of the Bureau of Parks and Lands , and such fees must be consistent with the goal of keeping entry affordable for Maine residents . In exchange , the Friends can keep 85 percent of entrance fee revenue , with the rest going to the State General Fund . An episode of the reality paranormal investigation TV series " Ghost Hunters " investigated Fort Knox for signs of a paranormal presence during one episode .