Columbiana is a city in Columbiana and Mahoning counties in the U.S. state of Ohio. The population was 6,384 at the 2010 census.The larger portion of the city, located in Columbiana County, is part of the Salem, OH Micropolitan Statistical Area, while the smaller Mahoning County portion is part of the Youngstown-Warren-Boardman, OH-PA Metropolitan Statistical Area.