NY 111 soon crosses the nearby Montauk Branch of the Long Island Rail Road just east of the Islip station, from where it continues north past various businesses and residences.

[3] Past Sunrise Highway, the route serves many blocks of residences prior to entering a cloverleaf interchange with the Heckscher State Parkway (exit 43).

Another north-northwesterly stretch follows, bringing the highway over another Long Island Rail Road line, this time the Ronkonkoma Branch.

Now out of Central Islip, the route traverses industrialized areas surrounding a large Y intersection with CR 17 (Wheeler Road) in Hauppauge.

NY 111 takes on the Wheeler Road name, and the route immediately enters an interchange (exit 56) with the Long Island Expressway (Interstate 495).

From here, the route bends northeast along Wheeler Road, paralleling the Nissequogue River as it serves the northern part of the town of Islip.

[7] The ultimately cancelled eastern extension of the Northern State Parkway would have crossed NY 111 just south of Village of the Branch at a point north of Mount Pleasant Road.