The United States used the Washington Meridian as the longitude reference for most states and territories created between 1861 and 1868 . The completion of the first permanent transatlantic telegraph cable on July 28 , 1866 , allowed the United States Naval Observatory at Washington , D.C. to be synchronized with the Royal Observatory at Greenwich . The need for a separate national meridian for the United States gradually faded , and in 1884 , U.S. President Chester A. Arthur called the International Meridian Conference in Washington , D.C. which selected the meridian of the Royal Observatory at Greenwich as the international Prime Meridian . On August 12 , 1912 , the United States adopted the Prime Meridian of Greenwich for all uses domestic and international
International Meridian Conference
International Meridian Conference
25th meridian west from Washington