- American Civil War: The Allegheny Arsenal explosion results in the single largest civilian disaster during the war; 78 workers killed.
- Battle of Antietam [Battle of Sharpsburg], bloodiest day in the American Civil War 23,110 die in first battle on Union soil
- Battle of Cumberland Gap, TN-evacuted by Federals
- Battle of Mumfordville, Kentucky, US Col J Wilder surrenders city
Day of the Week: Wednesday