Kaskaskia is a village in Randolph County, Illinois. Having been inhabited by indigenous peoples, it was settled by France as part of the Illinois Country. It was named for the Kaskaskia people. Its population peaked at about 7,000 in the 18th century, when it was a regional center. During the American Revolutionary War, the town, which by then had become an administrative center for the British Province of Quebec, was taken by the Virginia militia during the Illinois campaign. It was designated as the county seat of Illinois County, Virginia, after which it became part of the Northwest Territory in 1787. Kaskaskia was later named as the capital of the United States' Illinois Territory, created on February 3, 1809. In 1818, when Illinois became the 21st U.S. state, the town briefly served as the state's first capital until 1819, when the capital was moved to more centrally located Vandalia.

Randolph County is a county located in the U.S. state of Illinois. According to the 2020 census, it had a population of 30,163. Its county seat is Chester.