The area comprising New Castle Township was first settled by Europeans around 1800.

At the 2000 census there were 395 people, 180 households, and 113 families living in the township.

The racial makeup of the township was 99.24% White, 0.25% African American and 0.51% Asian.

[4] Of the 180 households, 21.1% had children under the age of eighteen living with them; 41.7% were married couples living together, 12.8% had a female householder with no husband present, and 37.2% were non-families.

For every one hundred females who were aged eighteen or older, there were 98.2 males.