Hillsboro is the county seat of Highland County, Ohio. Founded in 1807, Hillsboro was constructed to be the county seat. Before this community's establishment, New Market served as the Highland County seat of government.
Hillsboro grew relatively quickly, having 868 inhabitants in 1840. By 1846, the community contained three churches, two newspaper offices, fourteen stores, and an academy for men and another school for women. The town continued to grow over the next four decades. In 1880, 3,234 people resided in Hillsboro, with approximately one-third of the townspeople being school-aged children. One of the principal reasons for this growth was Hillsboro's location of two separate railroad lines. The town became a center of agricultural trade. In 1886, most of Hillsboro's manufacturing businesses produced items, including flour, carriages, and lumber, for farmers living in the surrounding countryside. Hillsboro's largest employer was J.M. Boyd & Company, with twenty-one employees. This firm processed flour. The town also contained three newspaper offices, eight churches, and three banks in 1886.
During the twentieth century, Hillsboro continued to serve as Highland County's urban center. Farmers continued to rely upon Hillsboro's businesses to meet their needs. In 2000, Hillsboro had a population of 6,368 people, making it the largest town in Highland County.