The Merrimack River (or Merrimac River, an occasional earlier spelling) is a 117-mile-long (188 km) 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 Gulf of Maine at Newburyport. From Pawtucket Falls in Lowell, Massachusetts, onward, the Massachusetts–New Hampshire border is roughly calculated as the line three miles north of the river.
The Merrimack is an important regional focus in both New Hampshire and Massachusetts. The central-southern part of New Hampshire and most of northeast Massachusetts is known as the Merrimack Valley.
Several U.S. naval ships have been named USS Merrimack and USS Merrimac in honor of this river. The river is also known for the early American literary classic A Week on the Concord and Merrimack Rivers by Henry David Thoreau.
