On February 12, 1820, the Ohio government authorized the creation of Seneca County. Residents named the county after the Seneca Indian tribe. Seneca County was originally part of territory set aside for Ohio’s Indian people by the Treaty of Greeneville. White settlement of the county occurred slowly, due to the Great Black Swamp occupying some of the land.
Seneca County is located in the northern part of Ohio. The county seat is Tiffin, which is the largest city in the county with a population of 18,135 people in 2000. Only 1.4 percent of the county’s 151 square miles are deemed to be urban. The county averages almost 107 people living in each square mile. Between 1990 and 2000, the county experienced a slight decrease in population. This is typical of Ohio’s more rural counties, as residents seek better opportunities in the state’s larger cities. In 2000, the county’s residents numbered 58,683 people.
Most of Seneca County’s residents find employment in manufacturing businesses, service industries, and retail positions. Over 1,300 farms also exist in the county. During the late nineteenth and early twentieth centuries, the county’s natural gas deposits led to a booming glass-making industry. Residents produced glass for both Fostoria and Tiffin. In 1999, the county’s per capita income was 21,695 dollars, with 9.6 percent of the county’s residents living below the poverty level.
Most voters in Seneca County claim to be independents, yet in recent years, they have supported Republican Party candidates at the national level.
The county is home to Heidelberg College.