New York State Route 129 (NY 129) is a 7.75-mile (12.47 km) long state highway in the western part of Westchester County, New York. The route begins at NY 9A (South Riverside Avenue) in the village of Croton on Hudson. NY 129 then travels through the towns of Cortlandt and Yorktown, running along the northern edge of the New Croton Reservoir. It passes under (southbound) and over (northbound) the Taconic State Parkway in Yorktown with no direct interchange. NY 129 ends in Yorktown at NY 118.

NY 129 begins at an intersection with NY 9A (South Riverside Avenue) in the village of Croton-on-Hudson. NY 129 proceeds northward from NY 9A along Maple Street, a two-lane commercial street through the village. At Van Cortlandt Park, NY 129 becomes residential, passing Croton Harmon High School as it bends to the northeast. At the junction with Grand Street, the Maple Street moniker ends, and NY 129 continues northeast on Grand Street, which is a two-lane residential street. The route continues northeast through the village, crossing several intersections with Quaker Bridge Road before becoming a wooded lane in the town of Cortlandt. In Cortlandt, NY 129 continues north as Grand Street, paralleling a local creek and entering Croton Dam Plaza.

Running along the western edge of the plaza, NY 129 bends north at a view of the New Croton Dam, continuing its way north alongside the New Croton Reservoir. NY 129 soon changes monikers to Croton Dam Road, passing east of the Croton Harman School District headquarters. At an intersection with East Mount Airy Road, NY 129 bends eastward along the reservoir, changing names to Yorktown Road and runs eastward alongside the reservoir. On a short stint away from the reservoir, NY 129 intersects with Croton Road before crossing over the Hunters Brook Bridge, where it crosses into the historic community of Huntersville. Continuing northeast from Huntersville, NY 129, now known as Croton Lake Road, bends through the town of Yorktown.

Through Yorktown, NY 129 is a two-lane residential street alongside the reservoir, soon making a gradual bend to the southeast into an intersection with County Route 131 (CR 131; Underhill Avenue), a former alignment of NY 131. At the junction with CR 131, NY 129 turns southward, soon winding its way southeast under the lanes of the Taconic State Parkway, and back alongside the New Croton Reservoir. After crossing under the Taconic, the route then drops back down to the level of the reservoir and passing a house reported to have been moved from Huntersville before it was flooded. Making several winds to the southeast, NY 129 connects to the Gate House Bridge, soon running eastward through Yorktown. Running along the reservoir, NY 129 intersects with NY 118 (Saw Mill River Road). This intersection serves as the eastern terminus of NY 129, as NY 118 continues east along the reservoir.

In 1908, the New York State Legislature created Route 2, an unsigned legislative route extending from the New York City line at Yonkers to the Columbia County village of Valatie. Route 2 initially followed modern NY 129, Croton Avenue, and NY 35 between Croton-on-Hudson and Peekskill; however, it was realigned on March 1, 1921, to use what is now NY 9A instead. NY 129 was designated to most of its current alignment as part of the 1930 renumbering of state highways in New York. It originally followed Croton Dam Road, the southern perimeter road around the New Croton Reservoir, while Croton Lake Road, the northern route, was designated as NY 131 by the following year. The alignments of NY 129 and NY 131 in the vicinity of the reservoir were flipped c. 1941 and the NY 131 designation ceased to exist by the mid-1940s.

Ramps from NY 129 to the Taconic State Parkway were removed by the East Hudson Parkway Authority in November 1969, to be replaced with a bridge that crosses over the parkway. This required a shutdown of NY 129 and required drivers going north to Underhill Road.

The entire route is in Westchester County.