Campbell is a city in eastern Mahoning County, Ohio, United States, along the Mahoning River. The population was 7,852 at the 2020 census. L…Campbell is a city in eastern Mahoning County, Ohio, United States, along the Mahoning River. The population was 7,852 at the 2020 census. Located directly southeast of Youngstown, it is a suburb of the Youngstown–Warren metropolitan area.