The Cochecho River or Cocheco River is a tributary of the Piscataqua River, 38.3 miles (61.6 km) long, in the U.S. state of New Hampshire. It rises in northern Strafford County and runs southeastward, through the town of Farmington and the cities of Rochester and Dover, where it provides hydroelectric power. Below the center of Dover, the river is tidal and joins the Salmon Falls River at the Maine border to form the Piscataqua.
Cochecho is an Abenaki word believed to mean "rapid foaming water," referring to the river's falls in downtown Dover. Settlers in 1623 adopted the name for the entire river and their settlement, Cochecho Plantation. It is believed the shift from Cochecho to Cocheco can be traced to a clerical error at the 1827 incorporation of the defunct Cocheco Manufacturing Company. Cocheco was adopted as the official spelling in a 1911 decision by the United States Board on Geographic Names. The river has also been known as the Dover River.
In 2015, the United States Board on Geographic Names received a formal proposal to change the spelling of the river from "Cocheco" to "Cochecho", which would have reversed the board's 1911 decision. The board, unable to decide, voted not to approve the name change after passing along the decision to New Hampshire's State Names Authority. A summary by the petitioner, a Wikipedia editor, may be found on the talk page.