Clark County covers 171 square miles. It was formed in 1836 from Frederick and later enlarged with land from Warren. The county was named for George Rogers Clark, conqueror of the Northwest. Lord Fairfax and Revolutionary hero General Daniel Morgan lived there. Loudoun County covers 519 square miles. It was formed in 1757 from Fairfax and was named for Lord Loudoun, titular governor of Virginia and head of the British forces in America from 1756 to 1758. OakHill, the home of President James Monroe, is in Loudoun County.