Grassy Key is an island that is part of Marathon, Florida so all of the conveniences of Marathon such as medical facilities, the airport, restaurants, schools, and shopping are close by. The Dolphin Research Center is located on Grassy Key and is a major attraction. Real estate in Grassy Key is primarily single-family homes—a lot of waterfront—within three primary communities: Crains Subdivision, Grassy Key Beach, and Sunset Bay.