Charles River was one of the eight original shires of Virginia. Named after the Charles River (for Charles I) the county was later renamed York after the name of the river was also changed.
New Kent was formed in 1654 from the upper section of York county, encompassing the watersheds of the Pamunkey and Mattaponi. Probably named after after the county of Kent in England it was possibly named after Kent Island in the Chesapeake Bay. William Claiborne, the most prominent man in the county in the mid-seventeenth century, had been born in Crayford parish in Kent. Claiborne was responsible for an abortive settlement on Kent Island in the early 1600s that was eliminated by the Maryland authorities.
More on Virginia "shires" here.
This series is called the "Geographic Transformation" because I think "Cartographic Transformation" doesn't really trip off the tongue.