Civil War Union Major General. Born in Columbiana County, Ohio, he was a professional soldier with a career in the United States military and a member of "The Fighting McCook's". He graduated from the United States Military Academy at West Point in 1852, 30th in his class. After graduation, he was assigned to the 3rd Infantry and served on the Western frontier. He fought Apache in New Mexico in 1857 and returned to West Point as a 1st Lieutenant and assistant instructor of infantry tactics from 1858 to 1861.When the Civil War began, McCook was appointed as Colonel of the 1st Ohio Infantry and commanded the regiment at Bull Run. His youngest brother, Charles Morris McCook, was killed in the battle. He was appointed as Brigadier General of U.S. Volunteers on September 3, 1861 and assigned to command a division in the Army of the Ohio. In 1862, he became Major General of U.S. Volunteers while his regular army rank was that of Colonel. He was placed in command of the 20th Corps and led them at the Battles of Perryville, Stones River, Tullahoma, and Chickamauga. He was relieved of corps command and assigned to command the Department of Eastern Arkansas in 1865. After the war, he briefly resigned and became an Indian Affairs investigator until October, 1865. He rejoined the Federal Army and was placed in command of the 26th Infantry. In 1880, he commanded the 6th Infantry, and in 1886, he was the commander of Fort Leavenworth. He retired from the army in 1895 at the rank of full Major General. During the Spanish American War, he was a war department investigator. He died in Dayton, Ohio in 1903 when he was 72 years old. Three of his eight brothers were generals during the Civil War. His father and another three brothers were officers. His father and three of the brothers were killed during battles in the war. Two of his cousins were also Civil War generals. The family was known as "The Fighting McCook's." The town of McCook, Nebraska was named after him.