Before Key Marco could be developed, several months of archaeological excavations and research had to be conducted. Four mounds were discovered on Key Marco, formerly known as Horr’s Island. The centers of the mounds were shells with layers of sand, charcoal, and more shells over the top. Radiocarbon dates for samples in the mounds yielded dates as far back as 4,000 years ago. Two burials were found in one of the mounds which yielded dates of around 3,400 years ago. This is the oldest known burial ground in the eastern United States. Key Marco’s high elevations and hilly roads which are uncommon to south Florida are a result of the shell mounds put in place by Calusa Indians over many centuries.
Captain John Foley Horr
Remains of Captain Horr's tabby home on Key Marco which is now a registered National Historical Site.
Captain Horr came to the island from Key West where he owned property that eventually became the U.S. Naval Base. Captain Horr also owned property in the Everglades. In 1880 Captain Horr was selected to take the Census. The Captain served as a collector of customs for the port and district of Key West from 1889 to 1893. In 1898, the Captain was made U.S. Marshall for the Northern District of Florida, a position he retained until 1913. In 1900, Captain Horr was the Republican nominee for Secretary of State of Florida; he also served as a delegate for the Republican National Convention in 1892 and again in 1900.
Captain Horr and his family used their home on Key Marco as a retreat, enjoying the quiet solitude of the uninhabited island. The Captain however, attracted others to his tropical paradise and eventually started a pineapple plantation, a small citrus grove, and a packing plant. At that time, pineapple was in heavy demand and the virgin, sandy soil produced a delicious fruit. As the plantation prospered, the island grew. Key Marco grew enough to house a school for a brief time in the early 20th Century.Captain Horr sold the property in 1923. It has remained uninhabited until now, awaiting the arrival of new settlers to rediscover this Island Treasure.
Captain Horr's great great granddaughter visits Key Marco:
http://marconews.com/news/2008/mar/24/vestiges-old-plantation-home-get-sized/