Sylvester Bonnaffon Jr. (September 14, 1844 – May 12, 1922) was a United States soldier who fought with the Union Army during the American Civil War as a first lieutenant with Company G of the 99th Pennsylvania Infantry. He received his nation's highest award for valor, the U.S. Medal of Honor, for his gallantry and leadership against Confederate troops during the Battle of Boydton Plank Road, Virginia on October 27, 1864. That award was conferred on September 29, 1893.