Potomac is an extinct incorporated town formerly located in Arlington County, Virginia. Today the dissolved town's former territory is located within the City of Alexandria after municipal annexation in 1930. As a planned community, its proximity to Washington D.C. made it a popular place for employees of the U.S. government to live. Potomac was loc…Potomac is an extinct incorporated town formerly located in Arlington County, Virginia. Today the dissolved town's former territory is located within the City of Alexandria after municipal annexation in 1930. As a planned community, its proximity to Washington D.C. made it a popular place for employees of the U.S. government to live. Potomac was located adjacent to the massive Potomac Yard of the Richmond, Fredericksburg and Potomac Railroad.