Antietam Creek is a 41.7 miles (67.1 km) tributary

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

 of the Potomac River

Potomac River

The Potomac River flows into the Chesapeake Bay, located along the mid-Atlantic coast of the United States. The river is approximately long, with a drainage area of about 14,700 square miles...

 located in south central Pennsylvania

Pennsylvania

The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...

 and western Maryland

Maryland

Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...

 in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, a region known as the Hagerstown Valley

Hagerstown Valley

Hagerstown Valley is located in Maryland in the United States. It is part of the Great Appalachian Valley, which continues northward as Cumberland Valley in Pennsylvania, and southward as Shenandoah Valley in West Virginia and Virginia....

. The creek became famous as a focal point of the Battle of Antietam

Battle of Antietam

The Battle of Antietam , fought on September 17, 1862, near Sharpsburg, Maryland, and Antietam Creek, as part of the Maryland Campaign, was the first major battle in the American Civil War to take place on Northern soil. It was the bloodiest single-day battle in American history, with about 23,000...

 during the American Civil War

American Civil War

The American Civil War was a civil war fought in the United States of America. In response to the election of Abraham Lincoln as President of the United States, 11 southern slave states declared their secession from the United States and formed the Confederate States of America ; the other 25...

.
The creek is formed in Franklin County, Pennsylvania

Franklin County, Pennsylvania

As of the census of 2000, there were 129,313 people, 50,633 households, and 36,405 families residing in the county. The population density was 168 people per square mile . There were 53,803 housing units at an average density of 70 per square mile...

, at the confluence of the West and East Branches of Antietam Creek, about 2.3 miles (3.7 km) south of Waynesboro, Pennsylvania

Waynesboro, Pennsylvania

Waynesboro is a borough in Franklin County, Pennsylvania, located northwest of Baltimore, Maryland, 67 miles southwest of Harrisburg, Pennsylvania, and north of the Mason-Dixon Line. The population within the borough limits was 9,614 at the 2000 census. When combined with the surrounding...

. The stream runs for about 0.5 mile (0.80467 km) before entering Washington County, Maryland

Washington County, Maryland

Washington County is a county located in the western part of the U.S. state of Maryland, bordering southern Pennsylvania to the north, northern Virginia to the south, and the Eastern Panhandle of West Virginia to the south and west. As of the 2010 Census, its population is 147,430...

.