Thomas White Simson was born in New York. On October 19, 1858, he enlisted into Company I, 1st Cavalry Regiment, which became the 4th Cavalry Regiment in August 1861. He served as a private and a corporal in the same company until March 27, 1863.
He was appointed a second lieutenant in the 6th U.S. Cavalry Regiment on February 27, 1863, but did not immediately move to the eastern theater to join his regiment. He was badly wounded in action with the 4th Cavalry at Franklin, Tennessee on April 10, 1863, and never fully recovered. Lieutenant Simson didn’t join the 6th Cavalry until August 1863. He was detached from the regiment on recruiting duty from April 1864 to February 1865. Simson was promoted to first lieutenant on February 3, 1865. He was retired on February 22, 1865 for incapacity resulting from wounds received in battle. Simson died October 26, 1865 in Elmira, New York of complications resulting from his wounds.