Youngest Medal of Honor Winner. His parents were born immigrants from England. His mother died when he was young, and his family lived briefly in Montreal, Canada in 1853, where his father remarried. Returning to Vermont in 1858, his father worked as an innkeeper. When his father enlisted in Company D, 3rd Vermont Calvary, in June of 1861, he joined his father in the same company, although he was denied pay due to his young age of 11. A year later, in 1862, he was approved to be paid with back wages to his date of enlistment. During the Peninsula Campaign, his unit was in a panicked retreat after a defeat by the Confederates in July of 1862 during the American Civil War. Many soldiers abandoned their weapons and gear. Johnston retained his drum and returned to Harrison's Landing at Berkeley Plantation, Charles City, Virginia. His superiors were so impressed by his dedication that they awarded him the Medal of Honor in 1863. He was the youngest recipient of this award. After this campaign, Johnson was wounded and transferred to the Invalid Corps in Baltimore. It was later reorganized as Company H, 20th Regiment Veteran Reserve Corps. He performed with the hospital band. He re-enlisted in February of 1864 and mustered out on August 31, 1865. After the war, he attended Norwich University for two years. In 1867, he unsuccessfully applied to the United States Military Academy. He married his wife, Nellie Murphy, in 1870, with whom he had five children. He worked as a machinist in Charlestown, Massachusetts, and may have also worked as a mariner. In July 1899, he attended the Medal of Honor Legion reunion in Vermont. In June 2012, a plaque honoring Johnston was placed at Berkeley Plantation, Virginia. His gravesite is unknown.