St. Clairsville or Saint Clairsville is a city in Belmont County, Ohio, United States, and its county seat. The population was 5,096 at the 2020 ce…St. Clairsville or Saint Clairsville is a city in Belmont County, Ohio, United States, and its county seat. The population was 5,096 at the 2020 census. It is part of the Wheeling metropolitan area. The seat of justice of Belmont County was originally known as Newellstown, and under the latter name was laid out in the late 1790s by David Newell. The name of the settlement was soon changed to St. Clairsville in honor of Northwest Territory Governor and Revolutionary War Major-General Arthur St. Clair.