Hahnville is a census-designated place (CDP) in and the parish seat of St. Charles Parish, Louisiana, United States. The population was 2,792 at the 2000 census. For the origin of Hahnville, see Michael Hahn (1830–1886).
Hahnville is located at 29°58′1″N 90°24′36″W / 29.96694°N 90.41°W / 29.96694; -90.41 (29.967081, -90.410129).
According to the United States Census Bureau, the CDP has a total area of 8.8 square miles (22.8 km²), of which, 7.8 square miles (20.2 km²) of it is land and 1.0 square miles (2.7 km²) of it (11.79%) is water.