William IV, Princely count of Henneberg-Schleusingen

William IV, Count of Henneberg-Schleusingen
Born	c. 1475
Died	24 January 1559 Salorno
Noble family	House of Henneberg
Father	William III, Count of Henneberg-Schleusingen (1434–1480)
Mother	Margaret (1451–1509), daughter of Henry the Peaceful, Duke of Brunswick-Lüneburg

Count William IV of Henneberg-Schleusingen (c.1475 – 24 January 1559), a member of the House of Henneberg, was a ruler of the County of Henneberg, within the Holy Roman Empire.

The son of William III of Henneberg, William inherited the County of Henneberg on 26 May 1480, when his father died, and reigned until his own death nearly eighty years later, on 24 January 1559.

William married Anastasia of Brandenburg, a daughter of Albert Achilles, Elector of Brandenburg.

In 1543–1544 William embraced the Protestant Reformation. In 1554 he signed a treaty of inheritance with John Frederick II, Duke of Saxony. William died in Salorno five years later. However, when his successor George Ernest, the last Count of Henneberg, died, both the Ernestine and the Albertine branches of the Wettin dynasty claimed his estates. In 1660 they were finally divided between the Ernestine duchies of Saxe-Weimar and Saxe-Gotha and the Albertine Maurice of Saxe-Zeitz, while the lordship of Schmalkalden went to William IV, Landgrave of Hesse-Kassel, honouring an inheritance treaty of 1360.