Sunol (formerly, Sunolglen) is an unincorporated census-designated place (CDP) in Alameda County, California, United States. The population was 1,332 at the 2000 census. The small, rural town of Sunol located along Niles Canyon is well known for its historic railroad system, on which the tourist railroad Niles Canyon Railway makes an in-town stop and the Altamont Commuter Express passes en route to San Jose and the Central Valley. The large Calaveras Reservoir lies south of Sunol.