The Suncook River begins at the outlet of Crystal Lake in the town of Gilmanton, New Hampshire.

Shortly before reaching the Merrimack River, the Suncook drops 70 feet (21 m) in 0.5 miles (0.80 km), a natural waterpower site that led to the growth of the village of Suncook.

On May 16, 2006, the Suncook River, responding to the highest rainfall amounts in at least 70 years (more than 8 inches (200 mm) dropped by a low-pressure system in three days on Concord, New Hampshire), rose to flood level and backed up behind an old mill dam, which produced a shallowly-sloping pool that overtopped a sand and gravel quarry, connected with a downstream section of channel, and cut a new shorter channel at 25–50 meters per hour in the town of Epsom.

[3] On September 3, 2018, there was news that work had begun to stabilize the Suncook River in its new course.

[4] In 1934, the American composer Alan Hovhaness (1911–2000), who spent time with his maternal family members in Pittsfield, New Hampshire, during his youth, wrote a fantasy for cello and piano entitled Legend of the Sunkook [sic] Valley (Op.