Cox was living in Darlington, Indiana, when he enlisted on January 30, 1864, as a 1st Sergeant and was mustered into “B” Co. IN 120th Infantry. He was promoted to 2nd Lieutenant on May 1, 1864, and to 1st Lieutenant on September 30, 1864. His discharge information is lacking.
The 120th was organized over the winter of 1863-64 and left the state on March 20, 1864. It first saw action at Rocky Face Ridge, joining in the charge which routed the Confederates. It then participated in the assault of Kennesaw Mountain and in the battle before Atlanta in July. It was in the siege of Atlanta and engaged at Jonesboro and Lovejoy’s Station. It moved in pursuit of Hood in October as far as Summerville. It was then detached from Sherman’s army, ordered to Nashville, and became involved in skirmishes at Columbia and in the battle at Franklin, where the 120th lost 48 men who were killed or wounded. When it reached Nashville, it took part in the battle of December 15 and 16, joining in pursuit of Hood’s retreating forces. The following year, the 120th proceeded to New Berne, North Carolina. It was in a sharp fight at Wise’s Forks when a furious assault was repulsed with heavy loss on the Confederate side. Joining the forces under Gen. Cox at Kinston, it moved to Goldsboro, meeting Sherman’s army which had arrived from Fayetteville.