G Lee Hearl has a beautiful site - both links worked for me. But for a shorter version of just the local counties, sort of the northern Virginia area, I composed this several years ago. I hope it helps anyone. Northumberland was formed in 1645 from the Indian District of Chicakacoan. Northumberland comprised present Lancaster (part of it), Westmoreland, Stafford, Prince William, Fairfax, Loudoun and Fauquier. In 1651 Lancaster was split off of Northumberland and York Cos. In 1653 Westmoreland was cut out of Northumberland, to run from the Machotick River upwards to the falls of the Potomac, to include present Stafford, Prince William, Fairfax. Loudoun and Fauquier. (The north and western part of Northumberland county was made into Westmoreland county in 1653, which was declared to run from Machotick River, "where Mr. Cole lives, and so upwards to the falls of the great river of Potomac, above the Necostins town" (the present site of Washington, DC), comprising the present counties of Westmoreland, Stafford, and Fairfax.) Old Rappahannock Co was split out of Lancaster Co in 1656. In 1664 Stafford was cut out of Westmoreland to include present day Prince William, Fairfax, Loudoun and Fauquier. In 1692 Old Rappahannock Co became extinct, as it was divided into Essex and Richmond Counties. In 1720 King George Co was formed from Richmond and maybe part of Westmoreland Cos. In 1731 Prince William was cut out of Stafford and included present day Fairfax, Loudoun and Fauquier. In 1742 Fairfax was created from northern Prince William Co, including present day Loudoun. In 1757 Loudoun was cut out of Fairfax, bounded on the south by northwestern Prince William. In 1759 Fauquier was cut out of Prince William County.