The 2020 census found 13,802 people in the township.

Located in the east central part of the county, it borders the following townships: The city of Celina, the county seat of Mercer County, is located in central Jefferson Township, and Grand Lake St. Marys occupies the township's southeastern quarter.

[4] It is one of twenty-four Jefferson Townships statewide.

[5] 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,[6] 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.