Fairfax County, with an area of 417 square miles, was formed in 1742 from Prince William and Loudoun and was named for Lord Fairfax, proprietor of the Northern Neck; Mount Vernon, George Washington’s home, is in this county. Prince William County, with an area of 345 square miles, was formed in 1730 from Stafford and King George and was named for William Augustus, Duke of Cumberland, second son of King George II; the first and second battles of Manassas took place in this county.