Issued from 1861-1862 during the U.S. Civil War in denominations of $5, $10, and $20, Demand Notes were used by the federal government to pay expenses, including the salaries of military personnel and government workers. They were the first widely circulated paper currency issued by the United States, and today remain the oldest valid currency. Demand Notes were nicknamed greenbacks because of the distinctive green ink on the reverse side of the note; the name was inherited by later forms of U.S. currency. Most of the notes were redeemed, leaving fewer than 1000 in existence.