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The Monongahela, US Army Department Jun 9, 1863 - Apr 6, 1864

US Dept. of The Monongahela created western Pennsylvania transferred from Middle Dept., Jun 9, 1863
Hancock Brooke and Ohio Counties in West Virginia transferred from US Middle Dept. to Dept. of the Monongahela, Jun 9, 1863
Columbiana Belmont and Jefferson counties in Ohio transferred from US Dept. of the Ohio to Dept. of the Monongahela, Jun 9, 1863
William T. H. Brooks Commander, Jun 9, 1863 - Apr 6, 1864
Hancock Brooke and Ohio Counties in West Virginia transferred from US Dept. of the Monongahela to Dept. of West Virginia, Oct 12, 1863

Columbiana Belmont and Jefferson counties in Ohio transferred from US Dept. of the Monongahela to Northern Dept., Jan 12, 1864
US Dept. of The Monongahela discontinued and merged into Dept. of the Susquehanna, Apr 6, 1864