Created on February 2nd 1863 the Union Army XXII Corps, made up of the Military District of Washington, and consisted of all troops garrisoned in Washington, DC. It included H Judson Kilpatrick’s Cavalry and three divisions of infantry. The XXII was under the command of Union Brigadier General James S Wadsworth. Its area of posting ran from Piscataway Creek, to Annapolis Junction, to the Monocacy River, south to the Bull Run Mountains and back by way of the Occoquan River. This area would expand by the end of the war to include Maryland and Virginia.
The XXII Corps held the defense of Washington, DC when Confederate General Jubal Anderson Early made his raid on the city in 1864. During the defense of Fort Stevens on July 11th 1864 as part of Early’s raid the XXII lost 73 men killed or wounded.