The Liesgau is an early medieval county (Gau) of the Duchy of Saxony, located in modern-day Germany. It lies on the south-west side of the Harz Mountains in present-day Lower Saxony. Its southern bound is near the town of Duderstadt and its northern bound is near Osterode, while its western bound is near the River Leine and its eastern bound corresponds to the present-day eastern border of Lower Saxony. It roughly conforms to the boundaries of the Osterode district.
The Liesgau is mentioned under the name Hlisgo in several documents from the 9th to 11th centuries. It was bordered by the following counties (list may be incomplete): Salzgau, Harzgau, Helmengau, Eichsfeld, Lochne, Suilberge. Its most important town was Pöhlde. In the 13th century, the Liesgau became part of the Duchy of Brunswick-Lüneburg, and later closely corresponded to the Grubenhagen subdivision of this duchy.
- The documents of Arnolf (Arnolfi Diplomata), King Arnulf of Carinthia, 6 July 889, Monumenta Germaniae Historica
- The deeds of Otto II and Otto of the III. (Ottonis II. et Ottonis III. Diplomata), King Otto III, 10 August 990, Monumenta Germaniae Historica
- Hand-Atlas in the History of the Middle Ages and Modern Times, Gaue of Saxony and Northern Thuringia