The unsigned Middlesex County segment begins at the intersection of Park Avenue and Maple Avenue in South Plainfield. The county route, not signed as CR 509 but rather CR 602, heads northeast on Maple Avenue through a residential neighborhood. After crossing Woodland Avenue, the road enters Edison and passes between two parts of the Plainfield Country Club. CR 602 breaks off the road at Inman Avenue leaving CR 509 on Old Raritan Road continuing northeast on a locally maintained road. At the UnionCounty line, the CR 509 designation ends and Raritan Road continues into Scotch Plains. The signed mainline portion of CR 509 begins at a complex intersection in the town of Westfield, west of Elizabeth. State Route 28 and Union CountyRoute 610come from Scotch Plains to the west on either side of the train tracks running along New Jersey Transit's Raritan Valley Line and criss-cross at a traffic circle a few hundred feet from the Westfield Train Station. CR 509 branches off in a northeast direction from Route 28 just after the state highway branches off of the circle and crosses under the tracks before continuing east. From its southern terminus to Elmer Street in Westfield, the road is town maintained. After cutting through downtown Westfield, CR 509 passes Fairview Cemetery on the right before coming to an intersection with CR 577, which splits off to the left before banking due north toward Mountainside, Springfield and U.S. Route 22. CR 509 turns right onto Springfield Avenue but quickly becomes Kenilworth Boulevard. For less than a mile, the route passes through Cranford, during which time County Route 615 splits off to the right. It crosses into Kenilworth, where it is signed simply as "Boulevard" while traveling nearly due east.. Once through downtown Kenilworth, CR 509 interchanges the Garden State Parkway at Exit 138 before crossing into Union. It dips southeast for a few hundred feet, then turns left onto Salem Road at a five-point intersection with Union County routes 616 and 619. Salem Road slowly bends back to the north, crossing State Route 82 near Kean University and over the Elizabeth River into Hillside, where it passes Vaux Hall Road and Hillside High School. CR 509 passes under US 22, but has no interchange. Traffic looking to access US 22 must turn right just beyond the overpass at Hillside Avenue, where access is provided near the Newark border. CR 509 turns left onto Hillside Avenue, while the road continues to a dead end at St. Peter's Park on the outskirts of Newark. After turning, CR 509 makes another quick turn, this time onto Chestnut Avenue. It passes over Interstate 78, to which access is available via Paine Avenue. The route continues as Coit Street, then Grove Street as it moves into Irvington and Essex County. Now in a heavily populated neighborhood, CR 509 crosses Springfield Avenue a little east of the end of the State Route 124 designation, and crosses several 600-series routes while closely paralleling the Parkway. It intersects CR 510 at the massive Cemetery of the Holy Sepulchre, then moves into Newark for about half a mile, then enters East Orange where it meets CR 508. Shortly thereafter, it interchanges with Interstate 280, providing access to Newark, the Oranges and the Parkway. CR 509 continues north into Bloomfield, where it turns left onto Franklin Street. It crosses back under the Garden State Parkway before moving into Passaic County, through the cities of Clifton and Paterson, where it ends at CR 504.
History
The two segments of CR 509 were previously connected through southern Union County via Raritan Road, Martine Avenue, West Broad Street, and Route 28.
Major intersections
CR 509 Spur
County Route 509 Spur was a county highway in Union County. The highway extended from Broad Street in Westfield to Route 124 in Springfield. The road is now part of a southern extension of CR 577. Major intersections
