La Vallée-du-Richelieu (French pronunciation: [la vale dy ʁiʃ(ə)ljø], The Valley of the Richelieu) is a regional county municipality in the Montérégie region in southwestern Quebec, Canada.

Dramatically different from the mountainous terrain to the south, the river valley is a vast plain that has been developed with extensive farmlands.

In the 21st century, the Richelieu River is very popular for both U.S. and Canadian recreational boaters, providing a connection that can bring boaters all the way from the outlet of the Saint Lawrence River to New York Harbor.

A number of old fortifications exist dating back to the 17th century; they were built by the French in an effort to try to prevent the Iroquois from using the river as a way to attack the French settlers in the area.

Fort St. Anne Isle La Motte, Vermont in Lake Champlain is near the river's source.