Until 1 January 2007 Korsør municipality was a municipality (Danish, kommune) in West Zealand County on the west coast of the island of Zealand (Sjælland) in Denmark. The municipality covered an area of 75 km², and had a total population of 20.644 (2005). Its last mayor was Henning Erichsen, a member of the Social Democrats (Socialdemokraterne) political party. The main town and the site of its municipal council is the town of Korsør.
The West Motorway (Vestmotorvejen) runs through the former municipality and onto the Great Belt Bridge (Storebæltsbroen), which spans the Great Belt. On the other side of the strait the motorway becomes the Funen Motorway (Fynske Motovej) at the city of Nyborg.
Fishing and margarine production are economically important trades in this area.
Korsør municipality ceased to exist as the result of Kommunalreformen ("The Municipality Reform" of 2007). It was merged with existing Hashøj, Skælskør, and Slagelse municipalities to form the new Slagelse municipality. This created a municipality with an area of 571 km² and a total population of 76,185 (2005). The new municipality belongs to Region Sjælland ("Zealand Region").
Number of inhabitants as of January 1 of the following years:
- 1980 - 20.257
- 1985 - 20.786
- 1990 - 20.443
- 1995 - 20.092
- 1999 - 20.048
- 2000 - 20.330
- 2003 - 20.654
- Municipal statistics: NetBorger Kommunefakta, delivered from KMD aka Kommunedata (Municipal Data)
- Municipal mergers and neighbors: Eniro new municipalities map