CR 531 makes a short jog to the west where it becomes known as Plainfield Avenue, then turns to the north on Plainfield Road, crossing back into Edison, passing by St. Joseph High School.

Eastbound direction follows West 5th Street/East 5th Street and westbound direction follows West 4th Street/East 4th Street, which provides access to Plainfield Train Station serving NJ Transit's Raritan Valley Line.

The mainline of CR 531 jogs to the east for one block at Pearl Street before turning northwest onto Watchung Avenue.

[1] However, Somerset Street is a borough-maintained alternate route of CR 531 which travels through the central business district of North Plainfield.

Watchung Avenue and Somerset Street provide right-in/right-out access to both sides of US 22, however for through traffic along CR 531, an overpass located between the two legs of the route is used to cross US 22.

CR 531 turns northwest to continue on Hillcrest Road and crosses the Passaic River into Long Hill, Morris County.