He served in the U.S. Army artillery between 1893 and 1896. At the start of the Spanish-American War in 1898, he re-enlisted in the artillery division and served another six months.
Stephenson studied at St. Viator College in Bourbonnais, joined the Viatorian order and was ordained in 1915. He remained at the college for a few years teaching English and history.
When the United States entered World War I, Fr. Stephenson volunteered in August, 1917 as a chaplain for the Knights of Columbus. He was stationed first at Camp Custer in Battle Creek, MI, a military training facility.
In October, 1917, Fr. Stephenson was assigned to Camp Green in Charlotte, NC, and in March, 1918, to Camp Wadsworth in Spartanburg, SC. After a short stay there, he was assigned overseas and served in France until the end of the war.
Fr. Stephenson was discharged from the Army in September, 1919 and returned to his duties at St. Viator College.
Later in his religious life from 1927-1929, Fr. Stephenson became the chaplain at Hines Veteran’s Hospital in Maywood, IL, a very large institution with hundreds of disabled war veterans.
As a veteran who served veterans, Fr. William Stephenson embodied patriotism in the name of the Lord, Our God.