St. Mark's Episcopal Church stands six miles north of Sharpsburg, near the site of the Battle of Antietam on September 17, 1862, the bloodiest one-day battle in American history. About 23,000 Americans on both sides were killed, wounded, or missing, and for six weeks barns, houses, and churches like St. Mark's were used because of the wounded treated there; the churchyard is believed to hold unmarked graves of soldiers who died there. After the Battle of Gettysburg on July 1-3, 1863, Gen. Robert E. Lee's defeated Army of Northern Virginia passed nearby as it marched south to the Potomac River, heavy skirmishing occurred in the area, and the church again served as a hospital. The 8th Illinois Cavalry's regimental surgeon worked there while fighting took place in nearby Williamsport, five miles northwest. In August 1863, the congregation contributed $28.08 for sick and wounded soldiers in the country. Completed in 1849, the church was built with a balcony for slaves because many early members were slaveholders. After the Civil War, some African Americans continued to worship there, and several former slaves are buried in the churchyard to the left of the church next to the cemetery wall.
