The 3rd Regiment Maryland Volunteer Infantry was an infantry regiment that served in the Union Army during the American Civil War.
It was noted for its holding the high ground at the center of the line at Antietam as part of Stainrook's 2nd Brigade, Greene's 2nd Division of Mansfield's XII Corps.
[1] The 3rd Maryland Infantry was organized at Baltimore and Williamsport, Maryland, beginning June 18, 1861 for a three year enlistment under the command of Colonel John C. McConnell.
The regiment was attached to Dix's Division, Baltimore, Maryland, to May 1862.
1st Brigade, Sigel's Division, Department of the Shenandoah, to June 1862.
2nd Brigade, 2nd Division, II Corps, Pope's Army of Virginia, to August 1862.
1st Brigade, 2nd Division, II Corps, Army of Virginia, to September 1862.
2nd Brigade, 2nd Division, XII Corps, Army of the Potomac, to October 1862.
(Non veterans assigned to 1st Brigade, 1st Division, XX Corps, Army of the Cumberland, April to October 1864.)
2nd Brigade, 1st Division, IX Corps, Army of the Potomac, April to June 1, 1864.
3rd Brigade, 1st Division, IX Corps, Department of Washington, to July 1865.
The 3rd Maryland Infantry mustered out of the service on July 31, 1865.
Moved to Brandy Station, then to Bealeton and to Stevenson, Ala., September 24-October 4.
Guard duty on the Nashville & Chattanooga Railroad until April, 1864.
Battles about Dallas, New Hope Church, and Allatoona Hills May 26-June 5.
Ruff's Station, Smyrna Camp Ground, July 4.
Regiment joined IX Corps, Army of the Potomac, April 1864.
Boydton Plank Road, Hatcher's Run, October 27–28.