[1] In May 1861, Dunn enlisted in the 27th New York Volunteer Infantry Regiment and was mustered in as sergeant of Company C. He was captured by the Confederacy in the First Battle of Bull Run.
[2] In August, he reenlisted in the 109th New York Volunteer Infantry Regiment and was mustered in as captain of Company D. He was wounded in the Battle of Spotsylvania Court House in May 1864.
[3] In the Battle of the Crater, with Colonel Catlin and Major Stillson injured, Dunn took command of the Regiment.
In 1868, he was appointed superintendent of public documents published by Congress in Washington D.C., a position he held until 1875.
He also served as manager of the Equitable Accident Association, president of the board of trustees of the Binghamton State Hospital, and member of the city excise and police commission.
They had one daughter, Mabel E.[1] Dunn died at home on November 27, 1914, on his 74th birthday.