Department of the Monongahela

The Department of the Monogahela was a military department created by the United States War Department during the Gettysburg Campaign of the American Civil War.

On June 9, 1863, President Abraham Lincoln, responding to Robert E. Lee's impending invasion of Maryland and Pennsylvania, called for 100,000 volunteers from those two states, as well as West Virginia and Ohio, to help repel the invasion, with only about 33,000 recruits answering his call. The Secretary of War, Edwin M. Stanton, ordered the creation of two departments to organize these militia and defend Pennsylvania. The Department of the Susquehanna consisted of most of central and eastern Pennsylvania. The Department of the Monogahela consisted of western Pennsylvania, including Johnstown, the Laurel Highlands, and Erie, as well as Hancock, Brooke, and Ohio counties in West Virginia, and the Ohio counties of Columbiana, Jefferson, and Belmont. The headquarters were established in Pittsburgh, under the command of Maj. Gen. William T. H. Brooks, a combat veteran of the Union Army of the Potomac.