The "Wilhelmsorden" of Hesse-Kassel (or Hesse-Cassel) was instituted by the Elector Friedrich Wilhelm I on 20 August 1851 as a civil and military Order of Merit. It was composed of the three lower grades of the Order of the Golden Lion and a Grand Cross was added. In total the order was awarded more than 450 times in the 16 years of its existence.
On 1 August 1866, Hesse-Kassel was annexed by Prussia and on 3 October of that same year the Hesse-Kassellian orders were incorporated into the Prussian system of honours. On 27 August 1875 the Order was abolished. Although there were no new awards by the Prussian Kings in the 1866–1875 era, the exiled Elector Friedrich Wilhelm I. awarded the order approximately 8 times until his death in 1875.
The Order is not to be confused with the exclusive
- Military Order of William of the Netherlands
- The Wilhelm-Orden of Prussia.
- Maximilian Gritzner, Handbuch der Ritter-und Verdienstorden (Leipzig, 1893)
- Werner Sauer, Die Orden und Ehrenzeichen des Kurfürstentums Hessen-Kassel (Hamburg, n.d.)