Battle of Sharpsburg (Confederate)
Battle of Antietam (Union)
Army of the Potomac under McClellan [US] defeats the Army of Northern Virginia under Lee [CS], resulting in the bloodiest day in American history.
Union losses:12,401 men
2,108 dead
9,540 wounded
753 missing
Confederate losses:10, 406
1,546 dead
7,752 wounded
1,108 missing
Skirmishes at Shepherdstown, Ashby's Gap, Williamsport, and Hagerstown, as Confederates under A. P. Hill covered the retreat of the Army of Northern Virginia from Sharpsburg. Lee would keep a heavy cavalry presence in the area until October.