Green Key, named for the color of its abundant mangroves, was originally known as Deer Island. It was homesteaded in the early 1900s by J.G. "Gip" and Cora Brown, who built a home at the tip of the key. In 1930, a limerock causeway was constructed to provide access from the mainland. In 1970, the property was deeded for public use and a park was developed. In recent years, the park was named in memory of Green Key advocate Robert K. Rees, a former county commissioner.