The 2020 census found 2,666 people in the township.

Located in the southwestern corner of the county along the Indiana state line, St. Joseph Township borders the following townships: The village of Edgerton is located in the southern part of the township.

The St. Joseph River flows north to south through it.

[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.