The third USS Alligator was a schooner in the United States Navy. Alligator was laid down on 26 June 1820 by the Boston Navy Yard; launched on 2 November 1820; and commissioned in March 1821 – probably on the 26th – with Lieutenant Robert F. Stockton in command. On 6 June 1996, the site of its wreck was added to the U.S. National Register of Historic Places.