The Second Battle of Bull Run or Battle of Second Manassas was fought August 28–30, 1862, in Prince William County, Virginia, as part of the American Civil War. It was the culmination of the Northern Virginia Campaign waged by Confederate Gen. Robert E. Lee's Army of Northern Virginia against Union Maj. Gen. John Pope's Army of Virginia, and a battle of much larger scale and numbers than the First Battle of Bull Run fought on July 21, 1861, on the same ground.

Prince William County lies beside the Potomac River in the U.S. state of Virginia. At the 2020 census, the population was 482,204, making it Virginia's second most populous county. The county seat is the independent city of Manassas.