Salem is a city in northern Columbiana County and extreme southern Mahoning County, Ohio, United States. At the 2010 census, the city's population was 12,303. Salem is a principal city of the Salem, OH Micropolitan Statistical Area, which includes all of Columbiana County. The small portion of the city that extends into Mahoning County is considered part of the Youngstown-Warren-Boardman, OH-PA Metropolitan Statistical Area.