Cyrus Ballou Comstock (February 3, 1831 – May 29, 1910) was a career officer in the Regular Army of the United States. After graduating from the United States Military Academy at West Point in 1855, Comstock served with the Army Corps of Engineers. At the beginning of the American Civil War, he assisted with the fortification of Washington, D.C. In 1862, he was transferred to the field, eventually becoming chief engineer of the Army of the Potomac. In 1863 during the Siege of Vicksburg, he served as the chief engineer of the Army of the Tennessee.