Köthen Castle (German: Schloss Köthen) is a castle in the German city of Köthen (Anhalt). Situated in a relatively flat landscape, it was protected by a moat. Formerly a ducal seat, it now belongs to a foundation for the preservation of sites in Saxony-Anhalt.
The castle has connections with the composer Johann Sebastian Bach who was employed by Leopold, Prince of Anhalt-Köthen. It is one of the locations for Köthen's biannual Bach festival.
Since the nineteenth century the castle has housed an important bird collection which was sold to Frederick Ferdinand, Duke of Anhalt-Köthen by the ornithologist Johann Friedrich Naumann.
This architectural ensemble in the historical center of the city was the Residence of the Princes and Dukes of Anhalt from 1244 to 1847. After 1603, it was the seat of the Anhalt-Köthen line. In 1806, the principality was elevated to duchy. With the death of Duke Henry in 1847, the Anhalt-Köthen line became extinct.
In the 17th century it was the seat of the Fruitbearing Society, a society for the promotion of the German language.
Johann Sebastian Bach worked in Köthen during the period 1717-1723 as Hofkapellmeister of Prince Leopold. Bach's first wife Maria Barbara died in Köthen in 1720. His second wife Ana Magdalena was employed at the court as a singer at the time of their marriage in 1721. After the Bach family moved to Leipzig in 1723, Johann Sebastian continued to write occasional pieces for the court for a few years until the prince died.