The highway proceeds northeast through Mamaroneck as a two-lane residential street named Keeler Avenue, crossing through the Old Rye Neck neighborhood.

The route soon reaches a junction with Harrison Avenue, where it turns north off Keeler, leaving the Old Rye Neck neighborhood and soon the entire village.

Just after the junction with Halstead Avenue, the route crosses west of the parking lot for the Harrison Metro-North Railroad station and soon over the New Haven Line (Northeast Corridor) tracks.

The route bends northwest through a residential section of Harrison, reaching a junction with the Hutchinson River Parkway (exit 14).

[3] Within White Plains, NY 127 becomes a county-maintained highway, gaining the designation of CR 30[4] as it passes the Maple Moor Golf Course.

On March 17, 1910, the state awarded a contract to improve the 2.91-mile (4.68 km) segment of what is now NY 127 leading south from the White Plains–Harrison line.