William Butler was born in 1831 in New Castle, Ireland. He was the fourth-youngest son of Edward
Butler of Bohernagaul, in the County of Tipperary. At the age of thirteen, Butler was apprenticed to merchant James Leara, of Clonmel, for seven years. By 1859, Butler had immigrated to the United States and settled in New York City. Through his letters, it is known that he had two brothers and a sister also living in New York in the 1860s. On March 1, 1859, he enlisted in the 69th Regiment of the New York Militia as a lieutenant. He was discharged in August, but re-enlisted as a captain in November. He was discharged again in September 1862 but re-enlisted the following month. Butler eventually achieved the rank of a Major. He was wounded in a battle near Petersburg, VA on June 16, 1864. Butler died in August 1864 in a United States Hospital in Annapolis, MD.