[2] This township is named after war hero Stephen Decatur, Jr.

According to the United States Census Bureau, the township has a total area of 45.2 square miles (117 km2), all land.

As of the census[4] of 2000, there were 3,021 people, 1,114 households, and 885 families residing in the township.

There were 1,237 housing units at an average density of 27.4 per square mile (10.6/km2).

16.3% of all households were made up of individuals, and 7.3% had someone living alone who was 65 years of age or older.