Guernsey County is a county located in the U.S. state of Ohio. As of the 2020 census, the population was 38,438. Its county seat and largest city is Cambridge. It is named for the Isle of Guernsey in the English Channel, from which many of the county's early settlers emigrated.

Cambridge (CAM-bridge) is a city in and the county seat of Guernsey County, Ohio, United States. It lies in southeastern Ohio, in the Appalachian Plateau of the Appalachian Mountains about 75 miles (121 km) east of Columbus and approximately 124 miles (200 km) south of Cleveland. The population was 10,089 at the 2020 census. It is the principal city of the Cambridge micropolitan area and is located adjacent to the intersection of Interstates 70 and 77.