William was born In Jonesborough, TN on October 25, 1855 to James C. and Sophia Eliza (Byers) Cox. James was a farmer and merchant in Jonesborough, and they lived in the same household as Sophia's father, step-mother, and step-siblings. Sophia's father, Col. Charles Potter Byers, was the editor of The Vindicator, and her mother, Elizabeth Conway Sevier, was the granddaughter of John Sevier, the first governor of Tennessee. William had one older brother named Hugh Aiken, tho