Route 42 was originally designated in 1927 to run along the Black Horse Pike between Ferry Avenue in Camden and the present US 40/US 322 split in the McKee City section of Hamilton Township, Atlantic County. In 1953, the southern terminus was cut back to its current terminus in the Williamstown section of Monroe Township to avoid the concurrency it shared with US 322. After the completion of the North–South Freeway between Bellmawr and Turnersville in 1959, Route 42 was moved to this freeway, and the Black Horse Pike north of Turnersville became Route 168.
