According to the United States Census Bureau, the town has a total area of 295.6 square miles (765.6 km²), of which, 138.9 square miles (359.7 km²) of it is land and 156.7 square miles (405.9 km²) of it is water.
The Town of Southampton contains 7 incorporated villages and 16 unincorporated areas, which are called hamlets in New York state [REF].