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. Despite Roundhead's proximity to Indian Lake and the Great Miami River, which flows out of it to the Ohio River at Cincinnati, the community is drained by the headwaters of the Scioto River, which meets the Ohio River at Portsmouth.