After the retreat of the Wisconsin Glacier, a mighty glacial lake called Glacial Lake Passaic formed in this area that, about 15,000 to 11,000 years ago, extended for in length and was wide. The lake finally drained when a blockage of the Passaic River reopened. The Great Swamp is the remnant of the lake bottom and portions of the swamp lay in what now is the township. Once the lake drained, higher areas became a wooded area that was used for hunting, fishing, and farming by Native Americans. At the time of colonization by the Dutch it belonged to the Lenape tribes, but British colonists did their best to displace them westward.