United States Armies and Departments
in the Eastern Theater of the Civil War
April 1861

Department of the East (Pre-war)

Major General John E. Wool

All of the United States east of the Mississippi not in other departments.

Dept. of Washington (est. 4/9)

Lt. Colonel Charles F. Smith (4/9-4/28)

Colonel Joseph K. F. Mansfield (after 4/28)

The District of Columbia (including Alexandria County, Va.), and Maryland as far as Bladensburg.

Dept. of Pennsylvania (est. 4/19)

Major General Robert Patterson

Pennsylvania, Delaware, and Maryland not in the Depts. of Washington and Annapolis.

Dept. of Annapolis (est. 4/27)

Brigadier General Benjamin F. Butler
Maryland between Annapolis, Baltimore and Washington.