Originally, NJ 24 ran from Phillipsburg, New Jersey to Newark, New Jersey. In 1974, that route was split into New Jersey State Highway 57, a decommissioned section that is still signed as NJ 24 even though the road had never been state maintained, and New Jersey State Highway 124.
The current NJ 24 is a freeway that runs from an intersection with Interstate 287 (see Interstate 87) in Hanover, New Jersey to an intersection with Interstate 78 in Springfield, New Jersey. Beyond the I-78 intersection, the road was to continue eastward as I-278, but that 7.2-mile section between I-78 and the current end of I-278 has never been built.