[1][2] It is a tributary of the Connecticut River, which flows to Long Island Sound.

[3] The Ammonoosuc rises on the western slope of Mount Washington,[1] in Sargent's Purchase in the White Mountains of southern Coos County.

Leaving the vicinity of the Presidential Range, the river flows westwardly into Grafton County, where it turns southwestwardly.

Along its course the Ammonoosuc passes through Chandler's Purchase, Bean's Grant, and Crawford's Purchase; and the towns of Carroll, Bethlehem, Littleton, Lisbon, Landaff, Bath, and Haverhill to the village of Woodsville, where it flows into the Connecticut River.

According to the Geographic Names Information System, it has also been known as:[2] See also Defunct placenames of New Hampshire.