Lake Santee is an unincorporated town and census-designated place in Decatur and Franklin counties, Indiana, United States. As of the 2010 census, it had a population of 820.
Lake Santee was built up in the 1960s as a housing development centered on a reservoir of the same name.
Lake Santee is located at 39°24′36″N 85°18′27″W / 39.41°N 85.3075°W in southeastern Indiana. It is situated 13 miles (21 km) northeast of Greensburg and 12 miles (19 km) northwest of Batesville.
According to the U.S. Census Bureau, the CDP has a total area of 2.8 square miles (7.3 km2), of which 2.5 square miles (6.4 km2) is land and 0.35 square miles (0.9 km2), or 12.60%, is water. The water area consists entirely of Lake Santee, the reservoir.