Portsmouth, city, seat of Scioto County, southern Ohio, at the confluence of the Ohio and Scioto rivers; incorporated as a city 1851. It is a commercial, manufacturing, and transportation center; products include iron castings, wood products, mopeds, chemicals, and shoelaces. Shawnee State University (1986) is here, and many Native American mounds and a U.S. nuclear facility producing fissionable material are nearby. The community was founded in 1803 and is probably named for Portsmouth, New Hampshire. It developed as a transshipment point after the completion (1832) of the Ohio Canal, which linked it with Cleveland; it grew as a rail center in the 1850s. The city suffered major river flooding in 1937. Population 25,943 (1980); 22,676 (1990); 20,909 (2000).
