Determination of an exact location for a West Jersey/East Jersey borderline was often a matter of dispute, but the old provinces correspond roughly with northern and southern New Jersey today.
The Delaware Valley had been inhabited by the Lenape (or Delaware) Indians prior to exploration and settlement starting around 1609 by the Dutch, Swedish and English. Settlement of the West Jersey area by Europeans was thin until the English conquest in 1664.
The Dutch had established one or two Delaware River settlements but by the late 1620s had moved most of their inhabitants to Manhattan which became the center of New Netherland.
The development of the colony of New Sweden in the lower Delaware began in 1638. A fort was built near present-day Wilmington, Delaware at the mouth of the Christina River (named for Sweden's Queen Christina). Most of the Swedish population was on the west side of the Delaware, but after the New Netherland's Fort Nassau was re-established to challenge the Swedes, Ft. Elfsborg was established near present-day Salem, New Jersey. The Dutch defeated New Sweden in 1655.
see also: List of Governors of New Jersey
References: reference: Weslager, Clinton Alfred, Dutch explorers, traders, and settlers in the Delaware Valley, 1609-1644. Philadelphia, University of Pennsylvania Press, 1961.