Marion Township was formed in 1833. It lies in the extreme northwest portion of Allen County.

Geographically, it is the largest township in the county consisting of about 40 square miles of zoned land as of the 2010 census the population was 6,715 citizens, 2,820 of whom lived in the unincorporated portions of the township. Marion Township has 4,312 registered voters.

The township is responsible for maintaining 46 miles of roads.