The Native American population had been reduced by substantial numbers at the time that the first Europeans settled the valley.  At the time of settlement, the Minsi or Munsee, the northernmost branch of the Lenape, lived here.  There were many sites where they still lived, however.  Many of those remaining gradually migrated West. A few websites you can find out more:
Lenape Language Sound Files:
History of the Lenape:
Lenape from Wikipedia:
Who Stole the Tee Pee? (interactive exhibit):

“The Munsee originally occupied the headwaters of Delaware river in New York, New Jersey, and Pennsylvania, extending south to Lehigh river, and also held the west bank of the Hudson from the Catskill mountains nearly to the New Jersey line. They had the Mahican and Wappinger on the north and east, and the Delaware on the south and southeast, and were regarded as the protecting barrier between the latter tribe and the Iroquois. Their council village was Minisink, probably in Sussex county, N. J. According to Ruttenber they were divided into the Minisink, Waoranec, Warranawonkong, Mamekoting, Wawarsink, and Catskill. The Minisink formed the principal division of the Munsee, and the two names have often been confounded. The bands along the Hudson were prominent in the early history of New York, but as white settlements increased most of them joined their relatives on the Delaware. In 1756 those remaining in New York were placed upon lands in Schoharie County and were incorporated with the Mohawk. By a fraudulent treaty, known as the "Walking Purchase," the main body of the Munsee was forced to remove from the Delaware about the year 1740, and settled at Wyalusing the Susquehanna on lands assigned them by the Iroquois. Soon after this they removed to Allegheny river, Pa., where some of them had settled as early as 1724. The Moravian missionaries had already begun their work among then. (see Missions; Moravians), and a considerable number under their teaching drew off from the tribe and became a separate organization. The others moved west with the Delaware into Indiana, where most of them were incorporated with that tribe, while others joined the Chippewa, Shawnee, and other tribes, so that the Munsee practically ceased to exist as an organized body. Many removed to Canada and settled near their relatives, the Moravian Indians.”
From Handbook of American Indians, 1906