United States Armies in the East

April – August 1861

Lt. Colonel Charles F. Smith

Lt. Colonel Charles Smith

Colonel Joseph K. F. Mansfield

Colonel Joseph Mansfield

The Department of Washington was established on April 9, 1861. It consisted of the District of Columba including its original territory of Alexandria County, Virginia, and the State of Maryland as far as Bladensburg.The Department was charged with the defence of the national capitol and served as the assembly point for the thousands of volunteers pouring in from all over the North to build an army to end the rebellion.

While the creation of the Department of Northeastern Virginia temporarily made the Department of Washington a rear area sending supplies and reinforcements to McDowell, the defeat at Bull Run returned Washington to the front lines. But within days the Department was consolidated into what was to become the Army of the Potomac.

Organization of the Department of Washington

1861: April • May • June • July

Timeline of the Department of Washington, 1861

April 9 Department established under Lieutenant Colonel Charles F. Smith
April 27-28 Colonel Joseph K. F. Mansfield took over the department from Smith
May 24 Union troops under New York Militia General Charles W. Sandford cross the Potomac from Washington and occupied Alexandria, Virginia, to reduce the threat to Washington D.C.
May 27-28 The Department of Northeastern Virginia was created and assigned to Brigadier General Irvin McDowell.
July 21 The Federal defeat at the Battle of Bull Run returned Washington to the front line of the war.
July 25

Department was consolidated with the Department of Northeastern Virginia and the Department of Maryland to form the Military District of the Potomac.

August 17 Merged into the Department of the Potomac