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.Despite the name, South Portland was never part of the city of Portland, but rather part of Cape Elizabeth. It broke off in 1895. However, both Cape Elizabeth and Portland were once part of Falmouth. Cape Elizabeth, and by default, South Portland, broke away from Falmouth in 1765. South Portland is a principal city of the Portland – South Portland – Biddeford metropolitan area.