Resident Population in Seneca County, OH was 54.52700 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Seneca County, OH reached a record high of 62.70000 in January of 1979 and a record low of 54.52700 in January of 2023. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Seneca County, OH - last updated from the United States Federal Reserve on May of 2024.