St. Marys is a city in Camden County, Georgia, United States. The city is the gateway to Cumberland Island National Seashore, the largest of the Georgia Coast's barrier islands. The National Seashore's visitor center and boat access are both located at the St. Marys waterfront. The city is also home to the annual St. Marys Rock Shrimp Festival, the St. Marys Submarine Museum, the Kings Bay Naval Submarine Base, and to eight Ohio-class submarines. The population of St.