Cross Westchester Expressway to Saw Mill River Parkway Northward, I-684 begins as two separate spur routes. The primary spur, which is officially designated I-684, begins at the
White Plains–
Harrison line at exit 9A of the
Cross Westchester Expressway (
I-287) in
Westchester County, New York. The other, officially designated as
New York State Route 984J (
NY 984J) but signed as I-684 in the northbound direction, begins in Harrison north of exit 16A (formerly exit 26) on the
Hutchinson River Parkway. NY 984J has one independent exit with Manhattanville Road, which serves
Manhattanville College, before joining the spur to I-287. The spurs, I-287 and the Hutch, surround an
office park. From the junction of the two spurs, the Interstate Highway takes a straight course to the north-northwest through a wooded corridor with Century Country Club on the west and residences on the east. After the Barnes Lane overpass a mile and a half () north of the spurs, it veers to the north-northeast for a half-mile () before turning to the north alongside Rye Lake, part of
Kensico Reservoir, one of many that
provide water to New York City. It remains in an increasingly narrow strip of woods between the lake and
Westchester County Airport into its first exit, Airport Road, from its southern terminus.
NY 120 parallels the highway to the east. Just north of that exit, NY 120 crosses over the road. Immediately after this exit, I-684 crosses the Connecticut state line. Signage indicates this, but it retains its New York
reference markers as it curves more to the northeast for the next through wooded and swampy country in the western corner of
Greenwich. There is no exit in Connecticut. after it reenters New York, in the town of
North Castle, it reaches its next exit, where
NY 22 serves that community and the nearby hamlet of
Armonk. The short section of I-684 in Connecticut is owned by the
Connecticut Department of Transportation (CTDOT), but maintenance and repairs to the stretch are performed by the
New York State Department of Transportation (NYSDOT), with the cost of maintenance being reimbursed to New York by Connecticut. Past that exit, it bends even more to the northeast, continuing past houses, parks, and golf courses located amidst dense woodlands. At Byram Lake Reservoir, it returns to a northward heading for , crossing into the town of
Bedford. The highway then curves northeasterly and then to the northwest once the reservoir is past. The Arthur W. Butler Memorial Sanctuary, a private nature preserve, replaces it on the east of the highway. Just south of the exit for
NY 172, I-684 bends northwest again. Over the next , the Interstate curves gently back and forth, maintaining its generally northerly heading, as its
median strip widens slightly. The surrounding lands start to include some more cleared lots, larger estates that were once small farms. At the northern end of this section, a
rest area serves southbound traffic. The highway passes
Bedford Hills Correctional Facility for Women, one of New York's two main women's prisons, a short distance to its west, and then bends northwest into the most extensive junction since its beginning: the northern terminus of the
Saw Mill River Parkway.
Saw Mill River Parkway to Brewster The Saw Mill merges from the southeast, its two roadways forming
service roads flanking I-684 for the next mile () as it passes a southern extension of
Muscoot Reservoir just east of the hamlet of
Katonah. Entry from the Interstate to the parkway (and
NY 117, which has its northern terminus at the parkway just below the Interstate) is from the southbound lanes only. A half-mile () north of the merger, the frontage roads merge into the Interstate at the exit for
NY 35, serving Katonah and the hamlet of
Cross River to the east. After that exit, the electrified tracks of
Metro-North Railroad's
Harlem Line parallel the highway to the west. They cross into the town of
Lewisboro. north of that point, NY 22 parallels on the east. A northbound-only exit leads onto it, allowing access to
NY 138, which crosses the Interstate at the hamlet of
Goldens Bridge.
Its train station is prominently visible on the west side of the highway. North of that station is the
North Salem town line. NY 22 detours slightly eastward, away from the interstate, for . When it returns, the roads and the railroad tracks bend strongly to the northeast, following the
Croton River on their west. After , this brings them to I-684's next exit, at
NY 116, again for only northbound traffic but with southbound entry.
Purdy's station is also adjacent to the highway but is screened from view by a line of trees. A quarter-mile () to the north, NY 22 crosses under to the opposite side. A short distance later, the Harlem Line veers northwest, followed quickly by NY 22, as the Interstate veers northeast. The Hardscrabble Road exit serves both directions and, via NY 22, allows access to the nearby hamlet of Croton Falls. past that junction, I-684 crosses into
Putnam County and the town of
Southeast. Within a thousand feet () of the county line, the
Brewster rest area serves northbound traffic. Beyond, the highway turns slightly more to the east, then swings back to the north into its northern terminus at
I-84. An almost-complete
cloverleaf interchange guides traffic east to
Danbury, Connecticut, or west toward
Newburgh. Traffic continuing north remains on a controlled-access route, designated but
not signed as NY 981B, to the last signed exit with the
concurrent routes of
US Route 6 (US 6) and
US 202 adjacent to
East Branch Reservoir. The highway carrying both roads parallels I-84 at this point. Just past it, I-684 officially ends as NY 22 merges onto the freeway, having left the US 6/US 202 concurrency. NY 22 briefly continues north as a four-lane freeway before becoming a two-lane surface road by the at-grade intersection with
Sodom and
Old Milltown Roads. ==History==