Route 23 is a state highway in the northern part of New Jersey, United States. The route runs 52.63 mi (84.70 km) from County Route 506 and County Route 577 in Verona, Essex County northwest to the border with New York at Montague Township in Sussex County, where the road continues to Port Jervis, New York, as Orange County Route 15. Route 23 heads through Essex and Passaic Counties as a two- to four-lane surface road and becomes a six-lane freeway north of a complex interchange with U.S. Route 46 and Interstate 80 in Wayne. The freeway carries Route 23 north to a concurrency with U.S. Route 202. Past the freeway portion, the route heads northwest along the border of Morris and Passaic Counties as a four- to six-lane arterial road with a wide median at places, winding through mountainous areas and crossing Interstate 287 in Riverdale. The route continues northwest through Sussex County as a mostly two-lane surface road that passes through farmland and woodland as well as the communities of Franklin, Hamburg, and Sussex before reaching the New York state line, just south of an interchange with Interstate 84 and US 6 in Port Jervis, in Montague Township near High Point State Park.

Montague Township is a township in Sussex County, in the U.S. state of New Jersey, in the New York City Metropolitan Area. As of the 2020 United States census, the township's population was 3,792, a decrease of 55 (−1.4%) from the 2010 census count of 3,847, which in turn reflected an increase of 435 (+12.7%) from the 3,412 counted in the 2000 census. High Point, within Montague Township, is the highest elevation within New Jersey at an altitude of 1,803 feet (550 m) above sea level. Montague is also the northernmost municipality in the state of New Jersey.