South Portland is a city in Cumberland County, Maine, United States, and is the fourth-largest city in the state, incorporated in 1898. As of the 2010 census, the city population was 25,002. Known for its working waterfront, South Portland is situated on Portland Harbor and overlooks the skyline of Portland and the islands of Casco Bay. Due to South Portland's close proximity to air, marine, rail, and highway transportation options, the city has become a center for retail and industry in the region.