New York State Route 128 (NY 128) is a 5.53-mile (8.90 km) long north–south state highway in northern Westchester County, New York. The route connects the hamlet of Armonk to the village of Mount Kisco. The road passes by the municipal offices of the Town of North Castle.

NY 128 begins at an intersection with NY 22 (Armonk–Bedford Road), an arterial boulevard, in the hamlet of Armonk (within the town of North Castle). NY 128 proceeds north on Main Street, a two-lane commercial street, intersecting with an old alignment of NY 22, entering the town center for North Castle, where it maintains the commercial backdrop through town. Passing west of Wampus Brook Park, NY 128 intersects with Old Mount Kisco Road, an old alignment as it leaves the town center. NY 128 soon parallels the park and Wampus Brook on its way north, maintaining the Main Street moniker until an intersection with Old Mount Kisco Road. At that junction, the route becomes Armonk–Mount Kisco Road, making a large bend westward near Al Ehrmann Park.

Now running northwest, NY 128 crosses through North Castle as a two-lane residential roadway, paralleling Wrights Mill Road into Wampus Pond County Park. Through the parkland, NY 128 bends northwest, running along the northern edge of the park, and passing Wampus Pond. NY 128 soon enters the town of New Castle, where it changes names to Armonk Road on its way north, remaining a two-lane residential street. The route winds its way north via several bends, soon becoming a wooded roadway through New Castle. Residences remain spacious, paralleling NY 128 into the village of Mount Kisco. Now in Mount Kisco, NY 128 retains the name Armonk Road until a junction with Lexington Avenue, where NY 128 proceeds north on Park Avenue, which intersects with NY 117 (Main Street). This intersection serves as the northern terminus of NY 128.

NY 128 was assigned as part of the 1930 renumbering of state highways in New York. In the mid-1930s, NY 128 was extended southward to the Connecticut state line by way of an overlap with NY 22 and Greenwich Road. It was truncated back to its current southern terminus in the early 1970s. The former routing of NY 128 south of NY 22 was redesignated as NY 433.

The entire route is in Westchester County.