In 1911, Howard Coffin (owner of the Hudson Motor Company) purchased 20,000 acres (81 km²) of land on Sapelo Island and began developing it as a private resort for himself and friends. In 1922, he purchased what was formerly called Long Island and renamed it Sea Island. In 1928 he began an overnight inn and lodge named "The Cloister." In 1929, The Plantation golf course was built. The area was a magnet for industrialists of the era, as well as notable figures from all areas. The area was referred to informally as "Millionaire's Island," and the land on the island was privately owned by some of the wealthiest families in the United States. After the Great Depression, wealthy elites began to vacation in other areas, but The Cloister remained a spot with the most exclusive clients only. To the present day, land on Sea Island is controlled privately, and public access is limited. The island is owned by the Sea Island Company, operated by the Sea Island CEO, Bill Jones. The Sea Island Company also owns property off the island limits, on St. Simons Island.
In June 2004 (June 8–10), it hosted a summit of the Group of Eight leaders. As with previous sites of the G8 meeting, the venue is remote, easily secured, and has a history of luxurious accommodations. As part of the security measures, the Department of Homeland Security (DHS) designated the summit a National Special Security Event (NSSE). However, DHS also began to deal with another NSSE: the state funeral of former U.S. president Ronald Reagan.
In late 2004, the Sea Island Company closed their famous hotel, The Cloister. After 75 years of service the hotel was torn down to make room for a new one. The new Cloister hotel reopened on April 1, 2006, along the Black Banks River on the west side of Sea Island. The new hotel has many of the same architectural features as the former building, reminiscent of Addison Mizner design. The famous 1928 Spanish Lounge, for example, was dismantled and completely rebuilt in the new hotel. The Sea Island Beach Club, a resort facility accommodating the island's visitors from The Cloister and residents, was also rebuilt. The new facility opened on July 10, 2007.
A guard hut and gated entry were recently constructed on the causeway leading to Sea Island. Visitors and sightseers are no longer permitted; the entire island is now accessible only to homeowners, club members and guests of the resort.
Many streets on the island were previously maintained by Glynn County. In fact, the company deeded the roads to the county in the 1960s. Recently, however, the company asked the county to give up its rights to utility easements and various roads on the island in order to enhance security for the island's wealthy residents by way of restricted access. Sea Island Company recently built a fishing pier at Gascoigne Bluff on nearby St. Simons Island since the public will no longer be able to fish from the bridge over Black Banks River.
The island's zip code is 31561.