It serves residential areas until it crosses into Rye Brook, where the street makes a turn to the southeast and soon enters more commercialized neighborhoods.

The businesses give way to homes east of the junction, and NY 120A passes into the village of Port Chester just three blocks from Ridge Street near an intersection with Bowman Avenue (CR 104).

[4] Inside the village limits, maintenance of NY 120A shifts from the state to Westchester County, which inventories the route as CR 112.

[5] Continuing on, the road narrows to two lanes ahead of Port Chester's central business district, where NY 120A passes the Port Chester Public Library and the village's post office ahead of a junction with Pearl Street three blocks west of U.S. Route 1 and two blocks west of the Metro-North Railroad.

Here, NY 120A turns off Westchester Avenue and onto North Pearl Street,[4] becoming a village-maintained route in the process.

[5] Continuing on, the highway serves King Street School before crossing from Port Chester to Rye Brook several blocks later.

The foray into Connecticut ends soon afterward, and the route proceeds to straddle the state line for another 0.7 miles (1.1 km).

Another New York-maintained stretch in Greenwich, Connecticut, soon follows as the route veers north to bypass the grounds of Westchester County Airport.

[4] Past Rye Lake Road, NY 120A serves the Griffith E. Harris Golf Club and several mansions on its way back to the New York–Connecticut state line.