The 2020 census found 3,322 people in the township.

Located in the southeastern corner of the county, it borders the following townships: The village of Chickasaw is located in northern Marion Township, and the unincorporated communities of Cassella, St. Rose, Maria Stein, and Sebastian lie in the western, central, and northwestern portions of the township respectively.

Marion Local Schools and the historic Roman Catholic convent of the Sisters of the Precious Blood and the Shrine of the Holy Relics are located in Maria Stein.

[4] The township is governed by a three-member board of trustees, who are elected in November of odd-numbered years to a four-year term beginning on the following January 1.

There is also an elected township fiscal officer,[5] who serves a four-year term beginning on April 1 of the year after the election, which is held in November of the year before the presidential election.