The Castle of Coswig was mentioned first in 1187. There is no evidence for slav settlements before this date. In 1215 Coswig is called an "Oppidium". During this time it was one of the most important cities North of the river Elbe.
In the 16th century Coswig was already connected to a drinking water pipe from Wörpen. Weaving, pottery and farming played the most important role in economics. The city was nearly completely destroyed by Hispanic troops during the Schmalkaldic War.
From 1603 to 1793, Coswig belonged to Anhalt-Zerbst.
The Castle was constructed at the end of the 17th century. The railway station was inaugurated on 10 September 1841. In 1987 the city celebrated its 800th-year of existence.