In 1876 the Tortugas harbor light structure replaced the original 1825 lighthouse located on the parade ground of Fort Jefferson. It became apparent that the lighthouse was not effective when shipwrecks continued to occur. Located too far away from the other shoals and reefs, the Garden Key lighthouse was not bright enough or tall enough. In 1856, construction for a taller lighthouse on Loggerhead Key began and the original lighthouse on Garden Key continued to operate until it was seriously damaged by hurricanes in 1873 and 1875. By the time the lighthouse was removed and approval for the new one was authorized, Fort Jefferson had been under construction for 30 years. The light was mainly used as a beacon, since the much stronger light on nearby more adequately, Loggerhead Key guided ships around the treacherous reefs.  

Iron was used since brick could shatter and spread flying debris into the fort if hit by cannon fire. The use of iron also made it possible to build a sturdy, yet comparatively lightweight structure that required minimal surface area- important factors considering the tower’s location. The light house stands 37 feet above the terreplein and just over 80 feet from ground level below. The bottom tiers of the iron light house were built in a hexagonal shape. The top two tiers of the lighthouse are cylindrical, with an observation deck midway up and a windowed room at the top.   

Harsh marine conditions of Dry Tortugas have affected the structural integrity of the harbor light. General maintenance and repairs were completed in 1930s, 1970s, 1990s, and 2000s. The most recent repairs in 2021 disassembled the lighthouse and removed it to an off-site facility for repair and complete rehabilitation. The Harbor Light was returned in 2022.