frederick county was established in 1743 from parts of orange county, virginia. at that time, "old frederick county" encompassed all or part of four counties in present-day virginia — shenandoah, clarke, warren, and frederick. it also included five in present-day west virginia — hardy, hampshire, berkeley, jefferson and morgan. the virginia assembly named the new county for frederick louis, prince of wales. he was the oldest son of king george ii of great britain.