Established on August 20, 1798, the county is named for Federalist Senator James Ross of Pennsylvania.

[5] Ross County was described by Ephraim George Squier and Edwin Hamilton Davis as having almost "one hundred enclosures of various sizes, and five hundred mounds" in their book, Ancient Monuments of the Mississippi Valley (1848).

They described the Indian-built earthworks as ranging from 5 to 30 feet (1.5–9.1 m) in size, and enclosures of 1 to 50 acres (0.40–20.23 ha) large.

These included Serpent Mound, Fort Ancient, Mound City, and Seip Earthworks (both now part of Hopewell Culture National Historical Park), and Newark Earthworks.

Paint Creek drains the lower central part of the county, flowing eastward to its terminus with the Scioto at a point southeast of Chillicothe.

The county terrain consists of frequent wooded hills, with the intermediate level areas devoted to agriculture.

[7] The county's highest point is Farrell Hill, six miles (9.7 km) northeast of Bainbridge.

The last Democrat to win a majority in the county was Lyndon Johnson in 1964, while Bill Clinton won a plurality in 1996 and Barack Obama came within just 439 votes in 2012.

Ross is part of Ohio's 2nd congressional district, which is held by Republican David Taylor.

Students from the following affiliated Ross and Pickaway county districts attend the vocational school: Ohio University established a regional campus in Chillicothe in 1966.