On February 15, 1808, the Ohio government authorized the creation of Preble County. Residents named the county in honor of Edward Preble, a hero of the American Revolution.
Preble County is located in the western part of Ohio. Its western border helps form the boundary between Ohio and Indiana. The county seat is Eaton, which is the largest city in the county with a population of 8,133 people in 2000. Approximately seventy-three percent of Preble County's 425 square miles are covered in farms. Only 1.4 percent of the county is deemed urban. The county averages almost one hundred people living in each square mile. Between 1990 and 2000, the county experienced a 5.5 percent increase in population, as many residents of Cincinnati, in nearby Hamilton County, sought to escape the larger city's busyness. In 2000, the county's residents numbered 42,337 people.
Most of Preble County's residents find employment in agricultural positions. In the state, the county ranks fifth in hog raising and seventh in corn production. Manufacturing, retail, and government positions finish second, third, and fourth respectively. In 1999, the per capita income was 22,272 dollars, with eight percent of the county's residents living below the poverty level.
Most voters in Preble County claim to be independents, yet in recent years, they have overwhelmingly supported Republican Party candidates at the national level.
The county is home to the only remaining double-barreled cover bridge in Ohio. Known as the Roberts Covered Bridge, the structure has stood since 1829. Songwriter Benjamin Hanby ranks among Preble County's more prominent residents.