When William Henry Casto was born on 27 August 1848, in Council Bluffs, Pottawattamie, Iowa, United States, his father, William Casto, was 32 and his mother, Racheline I Cornog, was 37. He married Blanch Parrott about 1883, in Bluff Twp, Monroe, Illinois, United States. They were the parents of at least 4 sons and 1 daughter. He lived in Custer, Custer, Idaho, United States in 1910 and Challis, Custer, Idaho, United States in 1920. He died on 12 September 1922, in Hailey, Blaine, Idaho, United States, at the age of 74, and was buried in Hailey, Blaine, Idaho, United States.