Georgetown is part of the Seaford, Delaware, Micropolitan Statistical Area. Prior to Georgetown's position as the county seat of Sussex County it was located in Lewes on the Delaware Bay. Dutch colonists had set up Delaware's first colony there in 1631 and it remained the only significant settlement in Delaware for some time. When William Penn established the three lower counties of Pennsylvania, which are now Delaware, Lewes was the natural choice for the location of the Sussex County's Seat of Justice. Sussex County itself was not well defined until after 1760 when a dispute between William Penn's family and Frederick Calvert, 6th Baron Baltimore was finally settled after intervention from the Crown. This dispute had the effect of delaying discussion over an appropriate county seat while the more important argument over the county's borders continued. Earlier Charles Calvert, 5th Baron Baltimore had argued that the county ended with Lewes, while Penn's sons stated it continued into Fenwick Island, which it now does. The Mason-Dixon Line was surveyed as part the agreement between the Penns and Lord Baltimore and it has since defined the western and southern border of the county.