Adamsville is an unincorporated community in Ontwa Township within Cass County in the U.S. state of Michigan. History Originally named Adamsport, the town was established in 1832. In 1838 it merged with Sage's Mill, a populated place on the other side of a creek. Notes Unincorporated communities in Cass County, Michigan Unincorporated communities in Michigan Populated places established in 1832 1832 establishments in Michigan Territory