Louise Isabelle Alexandrine Augusta, Countess of Sayn-Hachenburg, Burgravine of Kirchberg, full German name: Luise Isabelle Alexandrine Auguste, Gräfin zu Sayn-Hachenburg, Burggräfin von Kirchberg (19 April 1772, Hachenburg – 6 January 1827, Vienna, Austrian Empire) was the Princess consort of Nassau-Weilburg (28 November 1788 – 9 January 1816) through her marriage to Frederick William, Prince of Nassau-Weilburg.
Louise Isabelle was born as the only child of Burgrave Georg Wilhelm von Kirchberg, Count of Sayn-Hachenburg and Princess Isabelle Auguste Reuss of Greiz, both members of an ancient German nobility.
As she was the only heir to her father Louise married Frederick William, Hereditary Prince of Nassau-Weilburg, fifth child and eldest surviving son of Charles Christian, Prince of Nassau-Weilburg and his wife, Princess Carolina of Orange-Nassau, on 31 July 1788 in Hachenburg. Frederick William succeeded to his father Charles Christian upon his death on 28 November 1788.
They had: