Founded in Apr 1, 1820, Seneca County is one of 88 counties in the state of Ohio. Historically, Seneca County was formed from Huron County. The city of Tiffin is the county seat. With FIPS code of 147, Seneca County has a population of 54,906 and area of 550.59 square miles (1,426 km2).
List of all cities in Seneca County, OH alphabetically
| City/Town | Postal Code | Area Code |
| Alvada, OH | 44802 | 419/567 |
| Amsden, OH | 44830 | 419/567 |
| Attica, OH | 44807 | 419/567 |
| Attica Junction, OH | 44807 | 419/567 |
| Bascom, OH | 44809 | 419/567 |
| Berwick, OH | 44853 | 419/567 |
| Bettsville, OH | 44815 | 419/567 |
| Bloomville, OH | 44818 | 419/567 |
| Buckeye Village, OH | 44807 | 419/567 |
| Caroline, OH | 44807 | 419/567 |
| Carrothers, OH | 44807 | 419/567 |
| Flat Rock, OH | 44828 | 419/567 |
| Fort Seneca, OH | 44883 | 419/567 |
| Fostoria, OH | 44830 | 419/567 |
| Green Springs, OH | 44836 | 419/567 |
| Ink, OH | 44883 | 419/567 |
| Kansas, OH | 44841 | 419/567 |
| Lykens, OH | 44818 | 419/567 |
| Melmore, OH | 44845 | 419/567 |
| New Riegel, OH | 44853 | 419/567 |
| Old Fort, OH | 44861 | 419/567 |
| Reed, OH | 44807 | 419/567 |
| Reedtown, OH | 44807 | 419/567 |
| Republic, OH | 44867 | 419/567 |
| Siam, OH | 44807 | 419/567 |
| Tiffin, OH | 44883 | 419/567 |