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.
This log details the road within Passaic County. The mileage log is from the start of the road at US 1/9/22 in Newark. For some reason, the mile markers in the NJDOT straight-line diagram do not agree with those posted on the freeway; the road appears longer in the field by about 0.18 mile.
| Mile | Street Name | Feature (South to North) |
| 8.90 | Entering Clifton City, Passaic Co. | |
| 8.90 | New Jersey Freeway | Third River {bridge} |
| 9.09 | New Jersey Freeway | Lackawanna Railroad {underpass} |
| 9.28 | New Jersey Freeway | NJ 3 {underpass} |
| 9.41 | New Jersey Freeway | Ramp from NJ 21 northbound to NJ 3 {underpass} |
| 9.47 | New Jersey Freeway | Ramp from NJ 3 to NJ 21 northbound {underpass} |
| 9.94 | New Jersey Freeway | Connector to River Rd, CR 624 {underpass} |
| 10.10 | Entering Passaic City | |
| 10.38 | NJ 21 | River Dr northbound, CR 624; connect to Brook Ave, CR 608 {overpass} |
| 10.78 | NJ 21 | River Dr northbound, CR 624; connect to Van Houten Ave, CR 614 {underpass} |
| 11.27 | NJ 21 | River Dr, CR 624 {overpass} |
| 11.41 | NJ 21 | Paulison Ave, CR 618 {underpass} |
| 11.56 | NJ 21 | Gregory Ave {underpass} |
| 11.66 | NJ 21 | River Dr, CR 624 {overpass} |
| 11.74 | NJ 21 | State St {underpass} |
| 11.82 | Entering Wallington Boro, Bergen Co. | |
| 11.82 | Next 0.16 mile is in Bergen County | |
| 11.98 | Entering Passaic City, Passaic Co. | |
| 12.07 | NJ 21 | Passaic St {overpass} |
| 12.16 | NJ 21 | Washington Pl {overpass} |
| 12.23 | NJ 21 | Jefferson St {overpass} |
| 12.32 | NJ 21 | Madison St {overpass} |
| 12.36 | NJ 21 | Hope Ave {overpass} |
| 12.60 | NJ 21 | Monroe St {overpass} |
| 12.66 | NJ 21 | Dayton Ave {overpass} |
| 13.22 | Entering Clifton City | |
| 13.52 | NJ 21 | Ackerman Ave {overpass}; Bergen CR 42 is 0.15 mile east |
| 14.24 | NJ 21 | US 46 {underpass} |
| 14.35 | NJ 21 | US 46 {merge} |
| 14.35 | NJ 21 ENDS, Clifton City | |