Lake Kankakee was a prehistoric glacial lake that formed about 14,000 years before present in the Kankakee River valley across northern Indiana and into Illinois as meltwater pooled between moraines and stagnant ice during the late Wisconsin glaciation. Covering more than 3,000 square miles at its greatest extent, it was divided into two open-water basins by the Iroquois Moraine. As it developed and later drained around 13,000 years before present, it left sands, gravel, loamy sediments, dune fields, and the vast Grand Kankakee Marsh. Its overflow also helped create the modern Illinois River through the Kankakee Torrent.