The Merrimack River (or Merrimac River, an earlier spelling that is sometimes still used) is a 110 mile (177 km)-long river in the Northeastern United States. It rises at the confluence of the Pemigewasset and Winnipesaukee rivers in Franklin, New Hampshire, flows southward into Massachusetts, and then flows northeast until it empties into the Atlantic Ocean at Newburyport. From the point where the river turns northeast in Lowell, Massachusetts onward, the Massachusetts–New Hampshire border is roughly parallel to the river, three miles north of it.
The Merrimack is an important regional focus in both New Hampshire and Massachusetts. In New Hampshire, the central-southern part of the state is known as the Merrimack Valley Region, and in Massachusetts, the "Merrimack Valley" refers to a cluster of towns and small cities in the northeastern part of the state.