Cumberland Island National Seashore Located in Saint Marys, GA TRAVEL BASICS - CAMPING - LODGING ACTIVITIES - FACILITIES - FEES/PERMITS (NPS Photo) IN BRIEF Cumberland Island is 17.5 miles long and totals 36, 415 acres of which 16, 850 are marsh, mud flats, and tidal creeks. It is well known for its sea turtles, abundant shore birds, dune fields, maritime forest, salt marshes, and historic ...