Johnston and Nicketti Buchanan Floyd had twelve children, one of whom was Dr. George Ben Johnston, prominent physician in Richmond who is credited with the first antiseptic operation performed in Virginia. Both the Johnston Memorial Hospital in Abingdon and the Johnston-Willis Hospital in Richmond are named after him.
Education
Johnston attended Abingdon Academy, South Carolina College at Columbia, and the law department of the University of Virginia at Charlottesville
Religion
He was converted after the marriage