Hesse (Hessen) Nobility
Hesse-Darmstadt was a German noble family.
Darmstadt was the residence (capital) of the ruling landgraves (1567–1806) and of the Grand Dukes of Hesse (1806-1918).
When the Hanau-Lichtenberg line was extinguished in 1736 a portion of the Grafschaft of Hanau-Lichtenberg was inherited by Louis IX, a grandson of the last Count - Johann Reinhard III. Louis IX ruled his inheritance under the regency of his father until he became of age in 1740. He then ruled his lands in his own right with a residence in the capital of that area, Buchsweiler (Bouxwiller, France). A royal residence was maintained there until 1765 when his wife moved her residence to Darmstadt. Louis IX maintained a residence at Pirmasens. Three years later on the death of his father, Louis IX became the Landgrave of Hesse-Darmstadt. (Note: This is a simplification of the jurisdiction of these lands and the residences of this royal family)
A history in English may be found at the Wikipedia article Landgraviate of Hesse-Darmstadt.
A map of "Hessen-Darmstadt 1567-1866" can be found at Landesgeschichtliches Informationssystem Hessen (LAGIS).
(German spelling with link to German wiki Ernst Ludwig)
(German spelling with link to German wiki Ludwig VIII)
(German spelling with link to German wiki Ludwig IX)
Walther, A.F. Briefwechsel der „Grossen Landgräfin“ Caroline von Hessen. 2 volumes. Wien: Wilhelm Braumüller, 1877. Digital images. Google Books. https://play.google.com/store/books/details?id=vjkBAAAAQAAJ : 2014. (This is the wife of Louis IX)