 According to the United States Census Bureau, the township has a total area of , of which is land and , or 1.45%, is water.Cass County had been originally organized by an act of the Michigan Territorial Council on November 4, 1829, as four townships while Lewis Cass was the territorial governor.Mason was included in Ontwa Township at the end of 1833, and at the start of 1834 Mason Township was formed into the same land area that it is today, which is less than the standard of most townships.