Horses gave way to steam in 1839, and the railroad was extended west, reaching Somerville at the beginning of 1842.

In 1849, it purchased the Elizabethtown & Somerville and adopted a new name: Central Railroad Company of New Jersey.

[1] From 1883 to 1887, the CNJ was leased to and operated by the Philadelphia & Reading Railroad, with which it formed a New York-Philadelphia route.

The primary rolling stock repair shops were located in Elizabethport, New Jersey along Trumbull Avenue.

Also in 1929 CNJ purchased a 30 percent interest in the Raritan River Railroad, a 12-mile (19 km) short line from South Amboy to New Brunswick.

[1] Following World War II, passenger traffic diminished, and was almost entirely commuter business, requiring great amounts of rolling stock for two short periods five days a week.

CNJ drafted elaborate plans for reorganization; they came to naught as neighboring railroads collapsed.

In 1963, Lehigh Coal & Navigation sold its railroad properties to the RDG, but the lease to the CNJ continued.

In 1964, the state of New Jersey began subsidizing commuter service, and the tax situation changed[specify] in 1967.

Over the years CNJ maintained an extensive marine operation on New York Bay, including a steamer line to Sandy Hook.

On April 30, 1967, CNJ's last marine service, the ferry line between Manhattan and CNJ's rail terminal at Jersey City, made its last run, which was also the last day for the terminal itself; the next day CNJ passenger trains began originating and terminating at the PRR station in Newark via the Aldene Connection, where New York City passengers could transfer to either PRR or Port Authority Trans-Hudson (PATH) trains.

In 1864 CNJ extended its railroad across the bay into Bayonne, and north to the Jersey City terminus.

CNJ operated several trains into Pennsylvania and other points west or south, in association with the RDG.