Landgraviate of Hesse-Darmstadt
Heinrich XX was born at Offenbach, Landgraviate of Hesse-Darmstadt, younger surviving son of Heinrich XIII, Prince Reuss of Greiz (1747–1817), (son of Heinrich XI, Prince Reuss of Greiz and Countess Conradine Reuss of Köstritz) and his wife, Princess Wilhelmine Louise of Nassau-Weilburg (1765–1837), (daughter of Charles Christian, Prince of Nassau-Weilburg and Princess Carolina of Orange-Nassau).