Northern Virginia Campaign
When the Civil War broke out, Crook accepted a commission as Colonel of the 36th Ohio Infantry and led it on duty in western Virginia. He was in command of the 3rd Brigade in the District of the Kanawha where he was wounded in a small fight at Lewisburg. Crook returned to command of his regiment during the Northern Virginia Campaign. He and his regiment were part of John Pope's headquarters escort at the Second Battle of Bull Run.