Official Languages: Hessian
Established: 1806 AD/CE
Disestablished: 1918 AD/CE
Hesse-Darmstadt was a member of Napoleon's Confederation of the Rhine during the Napoleonic Wars. Rapidly expanding during the mediatizations, Hesse-Darmstadt became an amalgamation of smaller German states, such as the Electorate of Cologne. The legal patchwork of the state culminated in a decree issued on 1 October 1806 by Louis I. The old territorial estates were abolished, which altered Hesse-Darmstadt "from a mosaic of patrimonial fragments into a centralized, absolute monarchy." The Duchy of Westphalia, which Hesse-Darmstadt had received in 1803, was ceded to the Kingdom of Prussia during the Congress of Vienna. However, Hesse-Darmstadt was compensated with some territory on the western bank of the Rhine, including the important federal fortress at Mainz.
The neighboring Landgraviate of Hesse-Kassel had backed Prussia against Napoleon and was absorbed into the Kingdom of Westphalia. At the Congress of Vienna, Hesse-Kassel was reestablished as the Electorate of Hesse. To distinguish the two Hessian states, the grand duchy changed its name to the Grand Duchy of Hesse and by Rhine (German: Großherzogtum Hessen und bei Rhein) in 1816.
In 1867, the northern half of the Grand Duchy (Upper Hesse) became a part of the North German Confederation, while the half of the Grand Duchy south of the Main (Starkenburg and Rhenish Hesse) remained outside. In 1871, it became a constituent state of the German Empire. The last Grand Duke, Ernst Ludwig (a grandson of Queen Victoria and brother to Empress Alexandra of Russia), was forced from his throne at the end of World War I, and the state was renamed the People's State of Hesse (Volksstaat Hessen).
After World War II, the majority of the state combined with Frankfurt am Main, the Waldeck area (Rhine-Province) and the former Prussian province of Hesse-Nassau to form the new state of Hesse. Excluded were the Montabaur district from Hessen-Nassau and that part of Hessen-Darmstadt on the left bank of the Rhine (Rhenish Hesse), which became part of the Rhineland-Palatinate state. (Bad) Wimpfen—an exclave of Hessen-Darmstadt—became part of Baden-Württemberg, in the district of Sinsheim. After a plebiscite on 29 April 1951, Bad Wimpfen was transferred from Sinsheim district to Heilbronn District. This change to Heilbronn was carried out on 1 May 1952.