Roundhead is an unincorporated community in southeastern Roundhead Township, Hardin County, Ohio, United States. Although it is unincorporated, it has a post office, with the ZIP code of 43346. Located at an altitude of 1,004 feet (306 m), it sits at the intersection of State Routes 117, 235, and 385, 2¾ mile (4½ km) north of the northeast corner of Indian Lake and 13 miles (24 km) southwest of the city of Kenton, the county seat of Hardin County.