Topsham is located at (43.932006, −69.953815) [REF].
According to the United States Census Bureau, the CDP has a total area of 11.2 square miles (29.0 km²), of which, 11.0 square miles (28.5 km²) of it is land and 0.2 square miles (0.4 km²) of it (1.43%) is water.