The Soucook River is a 29.2-mile-long (47.0 km) river located in central New Hampshire
in the United States
. It is a tributary of the Merrimack
River, which flows to the Gulf of Maine.The Soucook River begins at the outlet of Rocky Pond on the border between the towns of Canterbury and Loudon
, New Hampshire.
The river passes through the village proper of Loudon, crossing a small dam, and continues south along a rapidly developing suburban corridor on the outskirts of Concord
. There are extensive sand and gravel deposits filling the Soucook River valley, which has led to the creation of several large excavation operations close to the river. New Hampshire Route 106 parallels the river throughout its course, crossing the river four times.