William of Hesse-Philippsthal (born 29 August 1726 in Philippsthal; died: 8 August 1810, Philippsthal) was a member of the House of Hesse and Landgrave of Hesse-Philippsthal from 1770 until his death.

William was the eldest son of Landgrave Charles I of Hesse-Philippsthal from his marriage to Caroline Christine of Saxe-Eisenach (1699–1743), daughter of Duke John William III of Saxe-Eisenach.

William served in the Dutch army as General of the Cavalry and Governor of 's-Hertogenbosch.

William was also Komtur of the Knights Hospitallers of the Commandry of Łagów.

In 1806, the Landgraviate of Philippsthal was occupied by French troops and annexed to the short-lived Kingdom of Westphalia.