Kaskaskia is a village in Randolph County, Illinois, United States. In 2010 the population was only 14, making it the second-smallest incorporated community in Illinois. It was a major French colonial town of the Illinois Country. Its peak population was about 7,000 when it was a regional center. Kaskaskia became the capital of the Illinois Territory on February 3, 1809. In 1818, Illinois became the 21st U.S. state and Kaskaskia was its capital until 1819.
In April 1881, the Mississippi River moved its path to the east. This flooded most of the town. The river now passes east rather than west of the town. The state boundary line, however, remained in its original location. Kaskaskia is on a small part of Illinois west of the river. It can only be reached from Missouri.