Until 1 January 2007 Sydthy municipality was a Danish municipality (Danish, kommune) in the former Viborg County on the west coast of Vendsyssel-Thy, a part of the Jutland peninsula in west Denmark. It is on the north bank of the Limfjord. The municipality covered an area of 322 km², and had a total population of 11,239 (2005). Its last mayor was Arne Hyldahl, a member of the Venstre (Liberal Party) political party.