Fauquier County, named for Francis Fauquier, lieutenant governor of Virginia from 1758-1768, was formed in 1759 from Prince William County, and its county seat is Warrenton. United States Supreme Court Chief Justice John Marshall was born in this county. Col. John Singleton Mosby and his 43d Battalion Partisan Rangers were active here during the Civil War. Prince William County, named for William Augustus, duke of Cumberland and third son of George II, was formed from Stafford and King George Counties in 1730, and its county seat is Manassas. The two Battles of Manassas took place here in 1861 and 1862.