On February 23, 1863, Long was appointed colonel of the 4th Ohio Cavalry, a regiment which recently had surrendered to the Confederate raider, Brigadier General John Hunt Morgan. Long improved the morale of the regiment and led it in the Tullahoma Campaign. He commanded the regiment's brigade, the 2nd Brigade, 2nd Division, Cavalry Corps of the Department of the Cumberland between March 1863 and August 20, 1864, including service at the Battle of Chickamauga. Long was wounded in the left side at the Battle of Farmington, Tennessee, October 7, 1863. He was distinguished in the Atlanta Campaign where he suffered a head wound at the Battle of Jonesboro, Georgia, August 20, 1864 and wounds in the right arm and right thigh at the Battle of Lovejoy's Station, Georgia, August 21, 1864. Long received brevet grade appointments as major, lieutenant colonel, and colonel in the Regular Army of the United States for "gallant and meritorious services" at the Battle of Farmington and Battle of Fort Sanders (Knoxville) in Tennessee and Battle of Lovejoy's Station in Georgia, respectively.