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.
General Braxton Bragg [CS] tries to split General William Rosecrans [US] forces as they try to return to the safety of Chattanooga. A second day breakthrough at the Brotherton Cabin forces the federals into a retreat, halted only by the Rock of Chickamauga, General George Thomas on Snodgrass Hill
The bloodiest two days in American history cost the Federals 1,657 dead, 9,756 wounded, and 4,757 missing for a total of 16,170 casualties out of 58,000 troops. The Confederate losses were 2,312 dead, 14,674 wounded and 1,468 for a total of 18,545 out of 66,000 troops.
Phil Sheridan [US], with a force of 40,000 men, strikes Jubal Early's [CS] 14,000 man Confederate army north of Winchester. Sheridan simply overpowered the Confederates. General Robert E. Rodes was mortally wounded in the conflict.
Sterling Price, with 18,000 men, lays siege to Lexington, Missouri, with a federal force of 3.600 under Colonel James Mulligan. After fighting intensified on September 19, Mulligan surrendered on the 20th.