Sylvester Day was born in 1778, the son of Elkanah Day and Lavinia Merrill. He worked as garrison surgeon's mate in the United States Army in 1807, and was at Fort Michilimackinac from 1810 to July 17, 1812, when British forces took the fort during the War of 1812. After his parole by British forces, he travelled to Detroit, Michigan, where he worked as a surgeon until General William Hull surrendered the city to the British in August 1812. He remained in Detroit in order to help care for sick and wounded soldiers who were unable to leave with the rest of the American troops. On October 16, 1812, he left Detroit with American prisoners of war on the British Brig Adams , headed for Fort Erie. However, the United States Navy captured the Adams while en route to its destination, and forced Day to disembark before burning the ship and all of his personal effects. Following this incident, Day began a legal suit against the U.S. government in an attempt to gain reparations for the property he lost in the burning, especially his extensive medical library. The U.S. Army appointed Day a surgeon of the 4th Regiment of Infantry on March 13, 1813. He transferred to the 5th Infantry on May 17, 1815, and was on duty in Detroit, Michigan, until 1818. He worked as post surgeon at Fort Mifflin, Pennsylvania, from 1818 to 1820, and later became post surgeon for the Allegheny Arsenal. Day worked at other locations before his death at Allegheny Arsenal, Pennsylvania, in 1851. He had at least two children: Lavania (1802-1835) and Hannibal (1804-1891).