Shelby County is a county in the western portion of the U.S. state of Ohio. As of the 2020 United States Census, the population was 48,230. Its county seat is Sidney. Its name honors Isaac Shelby, first governor of Kentucky. Shelby County comprises the Sidney, OH Micropolitan Statistical Area, which is also included in the Dayton–Springfield–Sid…Shelby County is a county in the western portion of the U.S. state of Ohio. As of the 2020 United States Census, the population was 48,230. Its county seat is Sidney. Its name honors Isaac Shelby, first governor of Kentucky. Shelby County comprises the Sidney, OH Micropolitan Statistical Area, which is also included in the Dayton–Springfield–Sidney, OH Combined Statistical Area.