Located in the northern part of the county, it borders the following townships: Three incorporated villages are located in Allen Township: Statewide, the only other Allen Townships are located in Hancock, Ottawa, and Union Counties.

[4] The first settlers within the bounds of today's Allen Township were the families of Ephraim and Aaron Ireland.

[5] It was greatly reduced when the Mercer County line was extended to the south; approximately half of the township was split off to form that county's Granville Township.

The first school in the township was built in 1840, and the first church was an Evangelical congregation.

[6]: 565 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.