In 1897, as part of the Pioneer Jubilee year, William wrote a letter that states he and his wife, Tirza, "in the year 1850 with David Bennet Captain of our 50 and James Pace Capt. over the hundred." He and Tirza did not become acquainted until after arriving to Utah. The letter is available to view on Family Search.
William's father's surname was Fisk, but he and his mother, Minerva Sagers Fisk, both took the surname of her second husband (Howard) after she and her first husband, Ira Fisk, divorced. It is for that reason that William Riley's surname is listed as "Howard" in most historical sources.