On August 17, 1861, William L. Patterson was mustered into Company F, 1st Ohio Volunteer Infantry, for a three-year enlistment at Camp Corwin, near Dayton, Ohio, in the rank of First Lieutenant.
The 1st OVI began recruiting men for a three-year enlistment on August 5, 1861. The 1st OVI was at full strength by August 30, 1861.