Thomas Smith Arnold was born in Fairfield, New York, on November 16, 1831, and moved to Herkimer, New York, in the 1850s. He worked as a lawyer before enlisting in the 121st New York Infantry Regiment during the Civil War. He died of war wounds on May 19, 1863. He married his cousin, Celestia Mary Dean (1837-1924), in 1858. Their daughter, Etta Mary, was born on January 13, 1861, and married Gershom Willard Clark on October 20, 1897. After her husband's death, Celestia married Charles A. Clark, a lawyer from Oswego, New York; his children from a previous marriage were H. Austin and Emma.
From the guide to the Clark-Arnold letters, 1856-1890, 1856-1858, 1880-1890, (William L. Clements Library, University of Michigan)