Believe it or not, a short stretch of the road, which hugs the west bank of the Passaic River from Riverfront Stadium in Newark all the way to US 46 in Clifton, does enter Bergen County.
NJ 21 was built in several parts. Its original section assumed McCarter Highway in Newark in the 1930s. By 1961, it was extended northward to NJ 3 using the name “New Jersey Freeway”; in 1970, it was stretched another few miles, to River Drive in Passaic (exit 11). At that point, it hit an engineering logjam, as the river was literally in the way of the construction.
Actually, the river often flooded as it took a wide turn, and the Army Corps of Engineers was called in to fix the flooding. The river was rerouted to the east for a stretch between the Gregory Avenue and Market Street bridges connecting Passaic and Wallington. This required the demolition of a number of Wallington houses. The road was then built over the newly drained land; the stretch up to Monroe Street (exit 12) opened in 1974.
However, the statutory county and municipal lines were not moved. As a result, a 0.16-mile stretch of NJ 21 (as measured at the center line) crosses into Wallington. The NJDOT control section number, which is 1603 on either side of this stretch, is 0200 within it, with the 02 designating Bergen County.
As an aside, a Wallington water pumping station which used to be on the east bank of the river now found itself on the west bank and is visible from the highway near the northbound on-ramp from River Drive (CR 624).
The original plans for NJ 21 north of Passaic had the road crossing into Bergen County in the vicinity of Garfield and Elmwood Park, using a right-of-way that had been proposed for NJ 3 as early as 1931, when that highway used McLean Boulevard in Paterson and then cut through Clifton and Passaic before crossing the river at the Gregory Avenue bridge. It took 26 years for the 2½-mile “missing link” between Monroe Street and US 46 to be completed; the road finally opened in December 2000, on the Passaic side of the river.
The very short route log below includes only NJ 21’s Bergen County section. There are no structures in the county. The mileage log is from the start of the road at US 1/9/22 in Newark.
| Mile | Street Name | Feature (South to North) |
| 11.82 | Entering Wallington Boro, Bergen Co. | |
 This ramp is in Wallington, as is the highway. |
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| 11.98 | Entering Passaic City, Passaic Co. | |