New York State Route 35 (NY 35) is the principal east–west highway in the northern part of Westchester County, New York, carrying average daily volumes of around 16,500 vehicles. Its western terminus is at US 9 in Peekskill, while its eastern terminus is at the Connecticut state line in Lewisboro, where it becomes that state's Route 35.

NY 35 begins at an interchange with US 6, US 9 and US 202 (Briarcliff–Peekskill Parkway) in the city of Peekskill. NY 35, US 6 and US 202 are concurrent upon leaving the interchange on Main Street. Bending eastward through Peekskill, the routes cross over US 9 as a two-lane commercial street through the city. Entering the center of Peekskill, NY 35, US 6 and US 202 bend eastward as a two-lane city street, passing through a dense neighborhood of commercial businesses and apartment buildings, crossing through the Artist District and soon into the downtown portion. Crossing an intersection with North Division Street (unsigned County Route 63 (CR 63)), the routes continue eastward along Main Street to an intersection with Broad Street. At that junction, US 6 continues east along Main Street while NY 35 and US 202 bend southward along South Broad Street.

NY 35 and US 202 continue south through Peekskill, becoming a two-lane commercial/residential street, soon crossing an intersection with Crompond Road (unsigned CR 24). At this junction, NY 35 and US 202 turn east on Crompond, remaining county maintained as part of CR 24, becoming a two-lane residential street for several blocks. NY 35, US 202 and CR 24 continue eastward for several blocks, winding through the city of Peekskill for several miles. Paralleling US 6 to the north, the routes pass south of Beecher Park and enter a large residential complex. Near Dayton Road, the routes bend southeast, passing Hudson Valley Hospital Center, leaving the city of Peekskill and entering the town of Cortlandt. At this crossing, the CR 24 designation terminates.

NY 35 and US 202 continue eastward through the town of Cortlandt, entering the hamlet of Toddville, which consist of several residences. The routes, still named Crompond Road, makes a gradual bend to the east, remaining a two-lane residential road for a distance. After Locust Avenue, the route becomes commercial to the southern side, soon winding northeast into an intersection with the eastern terminus of the western segment of the Bear Mountain State Parkway. At this intersection, NY 35 and US 202 continues east along Crompond as a two-lane commercial street. Crossing into the town of Yorktown, bending southeast as Crompond, soon bending to the northeast. A short distance from the bend, NY 35 and US 202 intersect with the western terminus of the eastern segment of the Bear Mountain State Parkway, which connects to the Taconic State Parkway.

Continuing east from the Bear Mountain State Parkway, NY 35 and US 202 continue east, becoming a two-lane boulevard through a commercial stretch of Yorktown. The routes soon become surrounded by dense forest, entering a diamond interchange with the Taconic State Parkway. After crossing under the parkway, NY 35 and US 202 runs along the northern boulevard of Franklin Roosevelt Park as a two-lane residential roadway. After passing a church and cemetery on the northern side of the roadway, NY 35 and US 202 intersect with the southern terminus of NY 132 (Old Yorktown Road). After NY 132, the routes continue east along Crompond, bending southeast at Springhurst Road. After crossing under power lines, Crompond Road continues southeast, bending south through Yorktown.

NY 35 and US 202 continue south through Yorktown, bending southeast, becoming a two-lane residential/commercial mix. Entering downtown Yorktown, NY 35 and US 202 intersect with NY 118 (Saw Mill River Road). At this intersection, NY 35 and US 202 become concurrent with NY 118 along Saw Mill River, leaving Crompond behind. NY 35, US 202 and NY 118 proceed northward along Saw Mill River Road, proceeding north as a two-lane commercial street. At Ridge Street, the routes turn northeast, turning east through Yorktown. The three routes remain concurrent for several miles, crossing out of Yorktown for the town of Somers. A short distance after the crossing, the routes split, with NY 118 and US 202 proceeding north on Tomahawk Street while NY 35 continues east on Amawalk Road.

At this point, NY 35 begins running south of the Amawalk Reservoir, winding eastward past several residences, and the dam of the Muscoot River. At Lake Road, NY 35 bends southeast through Somers, winding through dense forests, passing east of the Mildred Lasdon Sanctuary. Making a curve to the northeast, the route passes west of Larson Park Arboretum, running along the northern end of it. Winding eastward for several miles, the route becomes residential, bending southeast at Van Rensselaer Road. This southwestern progression goes for a distance, winding into the hamlet of Whitehall Corners. In Whitehall Corners, NY 35 intersects with NY 100 (Croton Turnpike). At this intersection, the Amawalk Road moniker changes to Woods Bridge Road.

Now running north of the New Croton Reservoir, NY 35 continues eastward along Woods Bridge Road, a four-lane reservoir road, soon crossing over. Upon crossing the New Croton, the route enters the town of Lewisboro. Still named Woods Bridge Road, NY 35 remains a two-lane road running along the southern side of the New Croton Reservoir. A short distance after, the route crosses into the town of Bedford. In Bedford, NY 35 proceeds southeast as a four-lane road, where the route changes names to Cross River Road as Woods Bridge forks off. After that, NY 35 enters exit 5 of I-684. After I-684, NY 35 continues east along Cross River Road as a four-lane boulevard, crossing north of a small New Croton branch. As the branch disintegrates, the route enters an intersection with NY 22 (Goldens Bridge Road).

After NY 22, NY 35 reduces to two lanes through Bedford, continuing east as Cross River Drive, entering the Cross River Reservoir. Running along the northern shore of the Cross River Reservoir, NY 35 becomes a two-lane residential road, continuing east through Bedford. A short distance later, the route crosses back into Lewisboro, making a bend southeastward on Cross River Road. A short distance to the east, NY 35 intersects with NY 121 (Old Post Road). The two routes become concurrent, entering a rich neighborhood. After winding northeast, NY 121 forks north at an intersection with North Salem Road. NY 35 meanwhile continues east on Cross River Road, as a two-lane commercial road for a short distance. Near Mark Mead Road, NY 35 crosses into a residential street.

NY 35 bends northeast again through Lewisboro, making a gradual curve near Mead Street. The route becomes a two-lane road, running along the northern border of Lewisboro Town Park. After several more winds, the route intersects with the northern terminus of NY 124 (Spring Street South) and a fork from the mainline NY 124 a short distance later. After the forked portion, NY 35 bends southeast through Lewisboro, entering the large residential hamlet of South Salem. The route winds eastward for a distance, intersecting with the northern terminus of NY 123 (Smith Ridge Road). Just east of NY 123, NY 35 continues as Cross River Road until reaching the Connecticut state line. At this junction, NY 35 becomes CT 35 (South Salem Road), running east through Ridgefield.

The portion of modern NY 35 between Peekskill and Croton Avenue east of the city was originally designated as part of Route 2, an unsigned legislative route, by the New York State Legislature in 1908. The route was realigned on March 1, 1921, to enter Peekskill on modern U.S. Route 9 (US 9) instead. In the 1930 renumbering of state highways in New York, various sections of what is now NY 35 were assigned state route designations. From Peekskill to Amawalk, it became part of NY 116, which continued north from Amawalk on NY 100 (now NY 118). The portion from Yorktown to NY 22 in Katonah via Bedford Road and Jay Street in Katonah was an extension of NY 132. Lastly, the segment between NY 121 in Cross River and Smith Ridge Road east of South Salem was designated as part of NY 123.

In 1934, US 202 was created and routed along NY 116 from Peekskill to Somers. Farther east, NY 123 was extended westward along current NY 35 to NY 22 northeast of Katonah c. 1940. In the early 1940s, modern NY 35 in Westchester County was established, extending across Upper Westchester County on parts of NY 116, NY 132, and NY 123. All three routes were truncated to their current termini at this time. The western terminus of NY 35 was set at US 9 in Peekskill, creating a long overlap with US 202 that still exists today. The number 35 was chosen to match the existing route number in Connecticut. In the 1950s, several plans to build an expressway along the NY 35 corridor were studied, but none of these plans were built. NY 35 was moved onto its current alignment north of Katonah in the mid-1970s.

The entire route is in Westchester County.