Key Biscayne is an island town in Miami-Dade County, Florida, United States. The population was 12,344 at the 2010 census.
While there had been earlier schemes to develop a town on Key Biscayne, it wasn't until the opening of the four-mile (6 km) long Rickenbacker Causeway from Miami to Virginia Key and on to Key Biscayne in 1947 that the island was opened up to large scale residential development. The northern two-thirds of the island had been operated as the largest coconut plantation in the continental United States during the first half of the 20th century. In 1940 the Matheson family donated over 800 acres (3.2 km2) of their land to Dade County for a public park (Crandon Park) in exchange for a commitment that the county would build a causeway to the island. The remaining Matheson property, stretching across the middle of the island, was then sold off to developers. Starting in 1951, the Mackle Construction Company offered new homes on the island for US$9,540, with just US$500 down. A U.S. Post Office contract branch was opened, the Community Church started holding services in an old coconut-husking shed, and the Key Biscayne Elementary School opened in 1952.The area was incorporated as a new municipality in 1991 - the first new city in Miami-Dade County in over fifty years. Rafael Conte was elected the first mayor along with members of the founding Village Council including Clifford Brody, Mortimer Fried, Michael Hill, Luis Lauredo, Joe Rasco, and Raymond Sullivan. The municipality's first manager was C. Samuel Kissinger and the first clerk was Guido Inguanzo.