Robert A. Knox was born around 1845 in Tennessee to Ormond Knox and Susannah Mandana Adams. His father was a farmer and doctor who owned $5,500 of real estate and $13,905 of personal property in 1860. The family moved to Harrison County, Texas, in the late 1840s, and Knox attended school there. He enlisted in the Confederate army, possibly serving in the 21st Texas Cavalry. He died sometime after August 1863.