Koudekerk on the Rhine is a village center of Alphen aan den Rijn, South Holland. Until 1991 it was an independent municipality and the village has about 4300 inhabitants. Koudekerk is located on the north side of the Old Rhine. Koudekerk on the Rhine has been renamed since January 1, 1938, to distinguish it from the village of Koudekerke on the island of Walcheren in the province of Zeeland.

Koudekerk on the Rhine is an ancient village with a history beginning in the 12th century. It is now accessible by car via the N11 motorway. There is a bridge over the Old Rhine from Hazerswoude-Rijndijk to Koudekerk on the Rhine.

The monumental Gothic village church is one of the oldest buildings in Koudekerk on the Rhine. Near the Old Rhine is the only remnant of the former gatehouse of the former castle Groot Poelgeest, an octagonal tower. The former castle is also known as Horn House.

Around the Koudekerk on the Rhine there are also various polder mills, including the Hondsdijkse Mill and the Lagenwaardse Mill. The latter mill had to be moved by the construction of the HSL from its original location in Leiderdorp. In case of large water pollution, the mills can be used as a reserve template.

There are a total of 31 national monuments in Koudekerk on the Rhine.