Tenhassen is a name derived from the Sioux language meaning "the tree of sweet juice".

As of the census[1] of 2000, there were 253 people, 108 households, and 77 families residing in the township.

The racial makeup of the township was 98.81% White, 0.40% Pacific Islander, 0.79% from other races.

23.1% of all households were made up of individuals, and 16.7% had someone living alone who was 65 years of age or older.

About 6.6% of families and 7.0% of the population were below the poverty line, including 4.8% of those under the age of eighteen and 14.5% of those 65 or over.