Mound Key is rich in early Florida history. The island was developed over 2,000 years of the Calusa Indian civilization. The site likely began as a flat, mangrove-lined oyster bar that barely rose above the shallow waters of the Estero Bay. Located in the center of the estuary, food was easy to find. As the native population grew, the remains of their food were collected and heaped into middens.
Mound Key is believed to have been the cultural center for the Calusa, known as Calos. The Calusa had their first encounters with Europeans in the early 1500s when the Spaniards were exploring the Caribbean and peninsula of Florida. The first recorded European contact with the Calusa was in 1513 when Spanish explorer Juan Ponce de Leon landed in the area. In 1566, Spain's first Governor of Florida, Pedro Menenzez de Aviles was appointed at this site. This was also the site of the first Jesuit mission to the New World, San Antonio de Carlos. The Spanish period of the site was hard fought and short lived and was abandoned by 1569. However, with the Spaniards came diseases for which the natives had no immunity. This would lead to the demise of their population when combined with continued warfare with local tribes and the end of their once great society occurred around 1750.
However, this would not be the end of human occupation of the island. The site was frequented by pirates and fisherman throughout the next several decades until it was homesteaded by Frank Johnson in 1891. The Johnsons brought in other families to farm the island until the property was sold to the utopian Koreshans in 1905. Today most of the island is preserved as a State archaeological site.