Mainville is a census-designated place in Columbia County, Pennsylvania, United States. It is part of Northeastern Pennsylvania. The population was 134 at the 2020 census. It is part of the Bloomsburg-Berwick micropolitan area.

Columbia County is a county in the Commonwealth of Pennsylvania. It is located in Northeastern Pennsylvania. As of the 2020 census, the population was 64,727. Its county seat is Bloomsburg. The county was created on March 22, 1813, from part of Northumberland County. It was named Columbia, alluding to the United States and Christopher Columbus. The county is part of the Central Pennsylvania region of the state.