A division of the Principality of Anhalt, held by princes of the branch of Anhalt-Zerbst between 1396 and 1562, when the last Prince abdicated. The town of Köthen lies in the country between the Rivers Saale and Mulde, north of Halle.
In the partition of 1603 among the sons of Joachim Ernst, Köthen became the residence of the youngest of the five brothers. When his line died out in 1665, the Prince of Anhalt-Plötzkau moved to Köthen. His line, whose head became a Duke in 1807, survived the Napoleonic era but died out in 1847, when the Duchy passed to the senior (Dessau) line, with the agreement of the Duke of Anhalt-Bernburg.