County Route 577, abbreviated CR 577, is a county highway in the U.S. state of New Jersey. The highway extends 9.96 miles (16.03 km) from Springfield Avenue (Route 124) in Springfield Township to Bloomfield Avenue (CR 506) in Verona.

CR 577 begins at an intersection with Route 124 in Springfield Township near the western terminus of Route 82. The highway originally started further south, at the intersection of Broad Street and Springfield Avenue in Westfield; Broad Street and eastbound Springfield Avenue are CR 509, while CR 577 went west and north on Springfield Avenue, which becomes Meisel Avenue as it enters Springfield. This route was changed in the past from CR 577 to CR 509 Spur (although the old signage was often left intact) but may have been changed back. In downtown Springfield, where most of the major streets are one-way, Maple Avenue carries the nominal route northbound to the official southern terminus, while Meisel Avenue carries the southbound traffic.

From the official southern terminus, the route heads north as two-lane undivided Main Street, which is municipally maintained. The road runs through suburban residential development, passing over I-78 and crossing into Millburn in Essex County. In Millburn, CR 577 reaches a junction with CR 527, at which point the route turns east onto a one-way pair that is county maintained. Northbound CR 577 follows three-lane Millburn Avenue and southbound CR 577 follows two-lane Essex Avenue on this pairing, which passes through the commercial downtown of Millburn. At the end of the one-way pair, the route becomes four-lane undivided Millburn Avenue and continues east through a mix of homes and businesses. At the Wyoming Avenue intersection, CR 577 turns northeast onto that road while CR 630 continues along Millburn Avenue.

Wyoming Avenue, which is a two-lane road, carries the route over New Jersey Transit’s Morristown Line and into wooded residential neighborhoods a short distance to the east of the South Mountain Reservation. The road continues through Maplewood before crossing into South Orange, where it reaches CR 510. At this point, CR 577 turns east to form a brief concurrency with CR 510, which is four-lane South Orange Avenue. Upon splitting from that route, CR 577 continues northeast on two-lane Wyoming Avenue. The road enters West Orange and becomes Gregory Avenue. Here, the route crosses CR 508 prior to reaching the CR 660 junction.

At CR 660, CR 577 turns north onto Mt. Pleasant Avenue and crosses First Watchung Mountain as the road makes a turn to the west. This road is four lanes at first, soon narrowing to two lanes. After crossing the mountain, the route intersects Prospect Avenue, which it turns north onto. At this intersection, Prospect Avenue heads south as CR 677 while Mt. Pleasant Avenue continues west as Route 10. Along Prospect Avenue, CR 577 is a two-lane undivided road that turns into a four-lane divided highway as it passes through commercial areas. The route comes to an interchange with I-280 and becomes a five-lane undivided road past that point, with three northbound lanes and two southbound lanes. At the CR 611 intersection, CR 577 becomes three lanes with two lanes southbound and one lane northbound The road runs between homes and the Montclair Golf Course to the west and the Eagle Rock Reservation to the east before becoming two lanes and crossing into Verona. In Verona, CR 577 passes residences before reaching its end at an intersection with CR 506. Past this intersection, the road continues north as Route 23.

A spur route, County Route 577 Spur, existed, which is now Essex County Route 677, however some newer signage along the road has brought back the CR 577 Spur designation.