The first names proposed were "Charlestown", in honor of Charles W. Ingalls; and "Liberia", but Rufus Goddard suggested Sebewa, after Sebewa Creek, meaning "little river". The first township meeting was held at the home of Jacob Showerman, but no record of the meeting attendees or acts remains. A post office named "Sebewa" was established on January 24, 1851, with Benjamin Weld as the first postmaster. On April 14, 1854, the post office was moved from Weld's properties in the southwest part of the township to the Showerman settlement when Lucius Showerman was named postmaster. In 1857, the office moved to "The Corners". The name was changed to "Cornell" on July 8, 1861 but was changed back to Sebewa on February 16, 1881. The office was closed on November 15, 1913. According to the United States Census Bureau, the township has a total area of , of which is land and 0.03% is water. As of the census of 2000, there were 1,202 people, 406 households, and 332 families residing in the township. The population density was 33.6 per square mile (13.0/km²). There were 415 housing units at an average density of 11.6 per square mile (4.5/km²). The racial makeup of the township was 98.34% White, 0.25% Native American, 0.08% Asian, 0.25% from other races, and 1.08% from two or more races. Hispanic or Latino of any race were 0.92% of the population. There were 406 households out of which 40.4% had children under the age of 18 living with them, 73.2% were married couples living together, 5.4% had a female householder with no husband present, and 18.2% were non-families. 15.3% of all households were made up of individuals and 5.9% had someone living alone who was 65 years of age or older. The average household size was 2.96 and the average family size was 3.30. In the township the population was spread out with 29.9% under the age of 18, 8.3% from 18 to 24, 31.3% from 25 to 44, 20.1% from 45 to 64, and 10.4% who were 65 years of age or older. The median age was 34 years.