Brigadier General James Monroe Williams

The following Union Army units and commanders fought in the Battle of Monocacy of the American Civil War. The Confederate order of battle is shown separately.

Abbreviations used

Brigade	Regiment or other
First Brigade BG Erastus B. Tyler	1st Maryland Potomac Home Brigade (5 companies): Cpt Charles J. Brown 3rd Maryland Potomac Home Brigade: Col Charles Gilpin 11th Maryland: Col William T. Landstreet 144th Ohio (3 companies): Col Samuel H. Hunt 149th Ohio (7 companies): Col Allison L. Brown Baltimore Artillery (6 guns): Cpt Frederick W. Alexander Howitzer, B&O Railroad Blockhouse: Cpt William H. Wiegel
Cavalry Ltc David R. Clendenin	8th Illinois Cavalry: Ltc David R. Clendenin 159th Ohio Infantry (detachment; mounted): Cpt Edward H. Leib Detachment Mixed Cavalry: Maj Charles H. Wells Loudoun Virginia Rangers

Division	Brigade	Regiments and other
Third Division BG James B. Ricketts	First Brigade Col William S. Truex (w) Col William Emerson	14th New Jersey: Ltc Caldwell K. Hall (w) 106th New York: Cpt Edward M. Paine 151st New York: Col William Emerson 87th Pennsylvania: Ltc James Alonzo Stahle 10th Vermont: Col William Wirt Henry (w)
Third Division BG James B. Ricketts	Second Brigade Col Matthew R. McClennan	9th New York Heavy Artillery: Col William H. Seward Jr. (w) 110th Ohio: Ltc Otto H. Brinkley 122nd Ohio (detachment): Ltc Charles J. Gibson 126th Ohio: Ltc Aaron W. Ebright 138th Pennsylvania: Maj Lewis A. May

Leepson, Marc. Desperate Engagement: How a Little-Known Civil War Battle Saved Washington, D.C., and Changed the Course of American History (New York: Thomas Dunne Books), 2007. ISBN 0-3123-6364-8
Monacacy National Battlefield website
Composition and losses of the Union Forces at the Battle of Monocacy. The War of the Rebellion: A Compilation of the Official Records of the Union and Confederate Armies. United States War Department. Volume XXXVII, Chapter 49, pp. 201–203