On January 2, 1813, the Ohio government authorized the creation of Harrison County. Residents named the county after William Henry Harrison.
Harrison County is located in eastern Ohio, in the heart of Appalachia. It is predominantly rural, with less than one percent of the county's 404 square miles consisting of urban areas. The county seat is Cadiz, which, in 2000, was the county's largest urban center with a population of 3,308 people. Many residents of Ohio's rural communities are seeking better lives and more opportunities in the state's cities. This holds true for Harrison County. Its population decreased by 1.4 percent between 1990 and 2000, reducing the county's population to 15,856 people. The county averages just thirty-nine people per square mile, making it one of Ohio's least populated counties.
Farming is the largest employer in Harrison County, with residents ranking second in sheep raising in Ohio. Many other residents work in the mining industry, with the county enjoying large deposits of sandstone and limestone. The county used to have large coal deposits, but coal companies mined most of this resource during the late nineteenth and the early twentieth centuries. In 1999, the per capita income in the county was 23,833 dollars, with 14.6 percent of the people living in poverty.
Most voters in Harrison County claim to be independents, yet in recent years, they have supported Republican Party candidates at the national level by very small margins.
Among Harrison County's more prominent residents were United States Secretary of War Edwin M. Stanton, actor Clark Gable, and General George A. Custer. The Ohio Historical Society maintains a memorial to General Custer in New Rumley.