NY 100 diverges from I-87 just north of exit 5 and heads northeast, crossing over the Sprain Brook Parkway about 0.6-mile (1.0 km) beyond the split.

Central Avenue has an interchange with Tuckahoe Road shortly after the Sprain Brook Parkway.

The road continues through Yonkers in the area between the Grassy Sprain Reservoir and the Bronx River, with many retail establishments lining both sides.

Central Avenue continues out of the city of Yonkers into the Edgemont/Greenville section of the town of Greenburgh.

Access to I-287 (the Cross Westchester Expressway) and the Bronx River Parkway can be made in the vicinity of the 100/119 overlap.

NY 100 then splits off to the north using Hillside Avenue and Grasslands Road as it goes around the perimeter of Westchester Community College.

Bradhurst Avenue leads into the hamlet of Hawthorne within the town of Mount Pleasant, crossing over the Sprain Brook Parkway along the way.

From this junction, the roadway (carrying 9A and 100) is a four-lane expressway as it continues north alongside the Taconic State Parkway.

It has an interchange with NY 117 (Bedford Road) about 1.1 miles (1.8 km) north of the 9A/100 merge, with all exits and entrances on the left.

In its northern extremes, NY 100 roughly parallels the Croton Reservoir on the north side before meeting up with US 202 in the hamlet of Somers, where it ends opposite the Elephant Hotel.

The northernmost section of NY 100 runs along a part of the "Croton Turnpike", an early private toll road that was chartered in 1807.

NY 100 was extended south from the Yonkers line in the Bronx along Jerome Avenue to the Grand Concourse.

[15] The NY 100 designation was removed from New York City following the opening of the Major Deegan Expressway in 1956.

[20] In April 1956, the Westchester County Planning Commission recommended that a new expressway should be built along the current NY 100 north of White Plains.