Fort Knox was a US Army installation which was established late for the containing of gold bullion repository in the United States of America on Earth from the 19th through the late-22nd century, when it became a museum.
Located in the state of Kentucky, Fort Knox was known as Earth's largest repository of gold which supported the country's economy. At its peak, it held upwards of 50 metric tons of bullion, or over nine trillion U.S. dollars. As such, it had a reputation for being a very secure facility and considered virtually impenetrable.
During the late-22nd century, a New World Economy formed, money and hard currency became functionally obsolete. The facility then became a museum to showcase the history of its use. The facility's secure reputation continued, despite an attempt by Ferengi to break in during the mid-2360s.
In 2375, while planning a heist of a Borg transwarp coil, Captain Janeway of the USS Voyager used Fort Knox as a metaphor to explain the scale and the level of security around the prize they sought. Some of the staff did not understand what Janeway meant, requiring Tom Paris to explain. In light of this, Captain Janeway named their mission "Operation Fort Knox". (VOY: "Dark Frontier")
- According to the novelization of Star Trek: First Contact, following the Third World War, the gold reserves of Fort Knox had been depleted to the point of nonexistence.