Sanibel is an island and city in Lee County, Florida, United States. The population was 6,469 at the 2010 census, with an estimated 2018 population of 7,402. It is part of the Cape Coral-Fort Myers, Florida Metropolitan Statistical Area. The island, also known as Sanibel Island, constitutes the entire city. It is a barrier island – a collection of sand on the leeward side of the more solid coral-rock of Pine Island.