Richmond County, with an area of 204 square miles, was formed in 1692 from Old Rappahannock County and was named for the town of Richmond, Surrey, England. Sabine Hall and Mount Airy, noted old homes, are in this county. Northumberland County, with an area of 205 square miles, was originally an Indian district called Chickacoan. In 1648 it became Northumberland County, named for an English county. The mouth of the Potomac River is here.