1111-1474 an Imperial (Reichsunmittelbar) County of the Holy Roman Empire, although some times occupied by Denmark, and thereafter an Imperial Duchy, sometimes in personal union with Denmark, until the dissolution of the Empire in 1806.
Up to 1864 the Duchy of Holstein was part of the Deutscher Bund, though in personal union with Denmark (the King of Denmark being also Duke of Holstein). In 1864 Holstein became part of Prussia.