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, and Crooked River State Park. Its territory is immediately bordered by Kings Bay Naval Submarine Base, which is the home port for several. The population of St. Marys was 17,121 as of the 2010 Census.