Millerstown is an unincorporated community in eastern Johnson Township, Champaign County, Ohio, United States. It lies at the intersection of Heck Hill, Ward, and Zimmerman Roads, 2 ¹⁄₂ miles (4.0 km) north of U.S. Route 36. Nettle Creek, a tributary of the Mad River, flows past Millerstown. It is located approximately 4 miles (6½ km) northeast of the village of St.