Upper St. Clair is a township in Allegheny County, Pennsylvania, United States. It is located about ten miles south of Pittsburgh, Pennsylvania. The population was 20,053 at the 2000 census. The Township of Upper St. Clair was named in honor of General Arthur St. Clair, the ninth President of the United States in Congress Assembled under the Articles of Confederation. Upper St. Clair apartments for rent comparison page shows most up to date rent information on Upper St. Clair apartments and houses. Rent information is obtained from multiple rental sources but we cannot guarantee their accuracy.