Until January 1, 2007 Slagelse Municipality was a municipality (Danish: kommune) in the former West Zealand County, on the southwestern coast of the island of Zealand, in eastern Denmark.

Its last mayor was Lis Tribler, a member of the Social Democrats.

Slagelse has existed since the 1000s, and coins have been minted there since Cnut the Great's time.

Of the remaining population, approximately 10% lived in rural areas.

The last 5% lived in the towns of Havrebjerg and Kirke Stillinge.

The museum has a focus on trade, artisanry and local history.

The municipality consisted of thirteen parishes and fourteen churches.

It features the town's patron Saint Michael with the dragon, which is coloured green.