Sea Island is an affluent resort island located in the barrier islands just off The Atlantic coast of southern Georgia in the United States. The resort complex is located in an unincorporated Glynn County. Sea Island is part of the group of islands known as the Golden Isles of Georgia, which include Jekyll Island, St. Simons Island, and Little St. Simons Island. Visitors to the resort island travel across a long causeway that crosses marshland. This area was immortalized by 19th-century poet Sidney Lanier in 'The Marshes of Glynn" (1878).