David C. Cox was born on March 14, 1831, in Zanesville, Ohio, to Horatio and Ann Cox. His father was a merchant who owned $12,000 of real estate by 1850. He grew up and attended school in Zanesville, and by 1850, he was also working as a merchant. He married Alice Lee on November 6, 1856, and they had at least two children: Lee, born around 1857; and Julia, born around 1859. By 1860, he working as a railroad clerk in Bellaire, Ohio.
He supported the Republican Party, and he spent the Civil War serving as a clerk for Ohio’s secretary of state, state legislature, and governor. After the war, he served as an assistant adjutant general in Ohio before beginning work with the Internal Revenue Bureau. By 1870, he owned $2,500 of real estate and $5,000 of personal property. In the 1870s, he worked as Superintendent of Documents for the Department of the Interior and as a pension agent. He drowned in Chicago, Illinois, on December 23, 1882.