Born on September 8, 1844, in Sulphur Springs, Ohio, Koons was one of twelve children of farmers Abraham and Jane Koons. In 1862, Koons enlisted in the 123rd Ohio Volunteer Infantry Regiment. He fought in seventeen American Civil War engagements, including the battles of Winchester, Cedar Creek, and Appomattox. He was captured at the Battle of High Ridge and held prisoner until Robert E. Lee's surrender. He was mustered out in 1865 with the rank of corporal and returned to the family farm.