The 2020 census recorded 688 people living in the township.

Located in the northwestern corner of the county, it borders the following townships: No municipalities are located in Mississinawa Township.

[5] The first settler within the bounds of today's Mississinawa Township was Philip Reprogle, who arrived in 1833.

Its borders were later extended northward to include part of Gibson Township when the rest of that township became part of Mercer County.

[6] 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.