Kennebec is a town in Lyman County, South Dakota, United States. The population was 240 at the 2010 census. It is the county seat of Lyman County.
Kennebec is located at 43°54′15″N 99°51′46″W / 43.90417°N 99.86278°W / 43.90417; -99.86278 (43.904284, -99.862801).
According to the United States Census Bureau, the town has a total area of 0.9 square miles (2.2 km²), all of it land.