World History Maps Interactive Historical Atlas of the Civil War, detail page for:

Washington, US Army Department Apr 9, 1861 - after Jun 25, 1865

US Dept. of Washington created District of Columbia and Maryland transferred from Dept. of the East, Apr 9, 1861
Charles F. Smith Commander, Apr 9, 1861 - Apr 19, 1861
Pennsylvania and Delaware transferred from US Dept. of the East to Dept. of Washington, Apr 19, 1861
Robert Patterson Commander, Apr 19, 1861 - Apr 27, 1861
US Dept. of Pennsylvania created Pennsylvania Delaware and parts of Maryland transferred from Dept. of Washington, Apr 27, 1861
Joseph K. F. Mansfield Commander, Apr 27, 1861 - Aug 17, 1861
Parts of Maryland transferred from US Dept. of Pennsylvania to Dept. of Washington, Jul 25, 1861
US Division of THE POTOMAC created including Depts. Of Washington and Northeastern Virginia, Jul 25, 1861
US Dept. of The Potomac created Delaware and Maryland transferred from Dept. of Pennsylvania parts of Virginia included Dept. of Pennsylvania discontinued Depts. Of Washington Northeastern Virginia and Shenandoah discontinued absorbed by Dept. of the Poto, Aug 17, 1861

US Dept. of Washington recreated including areas adjacent to Washington DC, Feb 2, 1863
Samuel P. Heintzelman Commander, Feb 2, 1863 - Oct 14, 1863
Christopher C. Augur Commander, Oct 14, 1863 - after Jun 25, 1865

Parts of Maryland transferred from US Dept. of the Potomac to Dept. of Washington, Jun 21, 1864
St Marys county Maryland transferred from US Dept. of Virginia and North Carolina to Dept. of Washington, Jun 27, 1864
US MIDDLE Division created including Depts. Of Washington West Virginia and The Susquehanna plus Harpers Ferry Virginia, Aug 7, 1864