Cadiz is a village in and the county seat of Harrison County, Ohio, United States, located about 20 miles (32 km) southwest of Steubenville. The population was 3,051 at the 2020 census.

Harrison County is a county located in the U.S. state of Ohio. As of the 2020 census, the population was 14,483, making it the fifth-least populous county in Ohio. Its county seat and largest village is Cadiz. The county is named for General William Henry Harrison, who was later President of the United States.