Ash Township was organized out of Frenchtown by the legislative act of 1837.

All that portion of the township of Frenchtown, as now organized, (in the county of Monroe) which lies north-west of Stony Creek, in said county, be, and the same is hereby, set off and organized into a separate township, by the name of Ash ; and the first township meeting therein shall be held at the house of John M. Beaubien, in said township. (Acts of the Legislature of the State of Michigan; 1837)

The township's name was derived from a just awakened Arba Ash who blurted out his last name when roused from a nap during a formation meeting. In 1838, Ash Township embraced all that part of the county of Monroe lying northwest of Stoney Creek.