Wilhelm Heinrich, Duke of Saxe-Eisenach (10 November 1691 – 26 July 1741), was a duke of Saxe-Eisenach.
He was born in Oranjewoud, the eldest and only surviving son of Johann Wilhelm, Duke of Saxe-Eisenach and his first wife Amalie of Nassau-Dietz.
Wilhelm Heinrich first married Albertine Juliane of Nassau-Idstein (daughter George August, Count of Nassau-Idstein) in Idstein on 15 February 1713.
This marriage was childless.
He married his second wife Anna Sophie Charlotte of Brandenburg-Schwedt in Berlin on 3 June 1723, just eight months after the death of Albertine Juliane.
The second marriage was also childless.
Wilhelm Heinrich acceded to the duchy of Saxe-Eisenach in 1729 upon the death of his father and was succeeded by his second cousin, duke Ernst August I of Saxe-Weimar.
The personal union between Eisenach and Weimar created by this succession was only nominal until 1809, when the two patrimonies were formally united.