 Tenhassen Township was organized in 1865.Tenhassen is a name derived from the Sioux language meaning "the tree of sweet juice".According to the United States Census Bureau, the township has a total area of 36.6 square miles (94.9 km²), of which 32.0 square miles (83.0 km²) of it is land and 4.6 square miles (11.9 km²) of it (12.56%) is water.