The township takes its name from the South Branch of the Au Sable River, which flows nearly the length of the township, from the southwestern corner north and east to its mouth at the Au Sable River in the northern part of the township.

As of the census[1] of 2000, there were 1,842 people, 735 households, and 557 families residing in the township.

There were 1,615 housing units at an average density of 15.3 per square mile (5.9/km2).

There were 735 households, out of which 28.4% had children under the age of 18 living with them, 65.4% were married couples living together, 6.5% had a female householder with no husband present, and 24.2% were non-families.

20.4% of all households were made up of individuals, and 7.6% had someone living alone who was 65 years of age or older.