On April 4, 1862, President Lincoln created the Department of the Rappahannock from the larger Department of the Potomac, detaching the I Corps from the Army of the Potomac to form the basis of the new department. Its territory consisted of Virginia “east of the Blue Ridge and west of the Potomac River, the Fredericksburg and Richmond Railroad, including the District of Columbia and the country between the Potomac and the Patuxent Rivers.” The commander of the I Corps, Irvin McDowell, was promoted to Major General and authorized to command the department.
