A numbered cross street of the 1811 plan, at the western edge of Turtle Bay.
51st Street is one of the 155 cross streets of the Commissioners’ Plan of 1811, 60 feet wide like most numbered streets. East of Lexington Avenue lies Turtle Bay, named after a former cove of the East River. The cove may have been named for the turtles found there; other historians derive the name from a Dutch one, Deutal Bay, after its knife-blade shape.