- Southern Terminus:
- Purchase Street (NY 120) and Cross Westchester Expressway (I-287) in Purchase
- Northern Terminus:
- Purchase Street (NY 120) in Armonk
- 8.55 miles
NY 120A is a north/south route in Westchester County. Westchester Avenue, which is the service road of the Cross Westchester Expressway (I-287) for much of its length, splits off after its interchange with Purchase Street (NY 120), changing designation from CR 62 to NY 120A. Westchester Avenue runs east for about a mile to Port Chester. There, NY 120A turns northeast onto North Pearl Street which it follows for a few blocks parallel to US 1. Then, it turns north onto King Street. After a couple of miles, it touches the New York-Connecticut state line and runs along it. It has an interchange with the Hutchinson Parkway and the Merritt Parkway (CT 15) at the state line. North of the parkways, King Street crosses the border into Connecticut, although there is no signage to indicate so. It retains the NY 120A designation while in Connecticut, which is a very unusual arrangement. Eventually, it crosses back into New York, and NY 120A ends just over the border at Purchase Street (NY 120), just north of exit 2 of I-684. King Street continues north as NY 120. The entire length of NY 120A is a two-lane undivided road, except for a very short stretch where Westchester Avenue widens to four lanes.