Duke Wilhelm in Bavaria, full German name: Wilhelm, Herzog in Bayern (born 10 November 1752 in Gelnhausen, Palatinate-Birkenfeld-Gelnhausen; died 8 January 1837 in Landshut or Bamberg, Kingdom of Bavaria) was Count Palatine of Birkenfeld-Gelnhausen between 1789 and 1799 and first Duke in Bavaria from 16 February 1799 until his death in 1837. From 17 December 1803 to 20 March 1806, Wilhelm was titled Duke of Berg. Wilhelm was a great-grandfather of Empress Elisabeth of Austria through his son Duke Pius August in Bavaria.

Wilhelm was born on 10 November 1752 in Gelnhausen to John, Count Palatine of Gelnhausen and his wife Wild- and Rhinegravine Sophie Charlotte of Salm-Dhaun. In 1778, Wilhelm became an honorary member of the Bavarian Academy of Sciences and Humanities.