Josslyn Island Site in Lee County, Florida, is a large shell mound associated with the Calusa, formed during or shortly before European contact. Mapped in 1983 by archaeologists from the Southwest Florida Archaeological Society, the mound covered about 4 hectares, or 9.9 acres, and rose to more than 5 metres in places. Its shell deposits consist mainly of whelks and conchs, with oyster and clam shells notably absent. Rarely visited since the early twentieth century and preserved in unusually good condition, the site may contain important evidence about the people who created it. In 1978, it was added to the National Register of Historic Places.