When William Aaron Cox was born on 16 April 1884, in Longton, Elk, Kansas, United States, his father, Zeno Merritt Cox Sr, was 32 and his mother, Elizabeth Ann Haggard, was 29. He married Frances Fitz about 1905, in Longton, Elk, Kansas, United States. They were the parents of at least 3 sons and 3 daughters. He died on 28 August 1955, in Graham, Young, Texas, United States, at the age of 71.