Franklin Township covers (22) twenty-two square miles and is bordered by the irregular shoreline of Grand Lake, once known as the Grand Reservoir, to the north. Its east borderline is Auglaize County, with the west border Butler Township and the south border Marion Township. It is approximately (6) six miles in length, stretching from State Route 127 on the west to The Auglaize/Mercer County line. It covers nearly (3 1/2) three and one-half miles from its northern most boundary to its southern most boundary.

The township was organized December 7, 1841 with the first elections held on Christmas Eve 1841. The first settlers to Franklin Township were Stephen Sprague, Abraham and John Miller, and the Lacey, Beauchamp, and Johnson families. The Botkin family settled on the Big Chickasaw Creek. Other early settlers to the township were William Winter, the Ballinger, Bennett, Brandon, Long Preston, McGee, Buxton, Selby, Dabbelt, Dammeyer, Burdges, and Trim families. Isaac Ellis, another early settler, was the chief fur buyer in this part of the country. Descendents of these early settlers still reside in the township and the county.

At the time of settlement, the Big and Little Chickasaw Indian tribes occupied the township. Two township streams currently bear their names. The citizens of the township and the Indians lived peaceably. The Indians never gave settlers cause for alarm. They lived along side one another for many years.

This township was, and continues to be, one of the county's best farming districts. Grains were the crops of choice. From the beginning of settlement, the residents of the township belonged to the important Mercer County fair board.