William H. Clayton was born around 1837 in Clark County, Missouri, to Philip and Susan Clayton. His father was a farmer who owned $5,500 of real estate and $900 of personal property by 1860. The family moved to Upper Alton, Illinois, in the late 1830s. By the early 1860s, he was working as a farmer.
He enlisted in the Union army on August 7, 1862, and he mustered in as a corporal in company B of the 80th Illinois Infantry on August 25. According to his service records, he was 5 feet, 9 inches tall, with dark hair and gray eyes. The regiment took part in the Battle of Perryville, the Chattanooga campaign, and the Atlanta campaign. He was promoted to sergeant on January 1, 1863. In September 1864, he observed that “Most of the soldiers if they could would vote for Old Abe” in the presidential election of 1864. Clayton explained that he “like[d] McClellan…but I do not like the platform of the convention,” which declared the war a failure and called for a “cessation of hostilities.” He died of disease on May 5, 1865.