The Battle of Antietam , also known as the Battle of Sharpsburg, particularly in the South, was fought on September 17, 1862, near Sharpsburg, Maryland and Antietam Creek as part of the Maryland Campaign. It was the first field army–level engagement in the Eastern Theater of the American Civil War to take place on Union soil and is the bloodiest single-day battle in American history, with a combined tally of 22,717 dead, wounded, or missing.