Horr's Island is a significant Archaic period archaeological site located on an island in Southwest Florida formerly known as Horr's Island. Horr's Island is on the south side of Marco Island in Collier County, Florida. The site includes four mounds and a shell ring. It has one of the oldest known mound burials in the eastern United States, dating to about 3400 radiocarbon years Before Present (BP). One of the mounds has been dated to as early as 6700 BP. It was the largest known community in the southeastern United States to have been permanently occupied during the Archaic period.