Charles City, created in 1634, is one of the eight oldest counties in the state. It was named after the King at the time, Charles I.
The original title to the primary settlement planted by Sir Thomas Dale in this area in 1613 was Bermuda City. This plantation had the potential to outstrip Jamestown as settlement moved up the James River, but the later governors' support for Jamestown and the "massacre" of 1622 shifted the center of settlement back on the lower river.
Since the colony was dependent on royal support, it made sense to honor the King by naming five of the first eight counties after the royal family. The initial settlers in 1607 had already named Cape Charles after Prince Charles, when he was still the second son and it was not obvious he would become King. It's smart to hedge your bets...
Just 15 years after the county was named in his honor, Charles I ended up as the last King of England to be killed in a civil war. He was beheaded in 1649, after Cromwell and his army seized control of Parliament.
The romanticized flight of royalist "Cavaliers" associated with the losing side (as opposed to the Puritan "Roundheads" on the winning side) has given the University of Virginia its "Cavalier" mascot with the plumed hat.