The Harzgau was a medieval 'gau' county near the northeastern Harz mountains in the Eastphalia region of the Duchy of Saxony. It included the towns of Halberstadt, Quedlinburg, and Osterwieck, and was bounded by the Oker in the west, by the Großer Graben in the north, the Bode in the east, and the Harz in the south.