The Croton Aqueduct or Old Croton Aqueduct was a large and complex water distribution system constructed for New York City between 1837 and 1842. The great aqueducts, which were among the first in the United States, carried water by gravity 41 miles (66 km) from the Croton River in Westchester County to reservoirs in Manhattan. It was built because local water resources had become polluted and inadequate for the growing population of the city. Although the aqueduct was largely superseded by the New Croton Aqueduct, which was built in 1890, the Old Croton Aqueduct remained in service until 1955.

The Croton River is a river in southern New York with three principal tributaries: the West Branch, Middle Branch, and East Branch. Their waters, all part of the New York City water supply system, join downstream from the Croton Falls Reservoir. Together, their waters and the reservoirs linked to them represent the northern half of the New York City water system's Croton Watershed.