Most of the town was destroyed in April 1881 by flooding. During the flood, the Mississippi shifted to a new channel, running to the east of the town instead of to the west as before; the state boundary line, however, remained in its original location. Kaskaskia is therefore one of the few portions of Illinois west of the Mississippi. The old riverbed is now a creek or bayou.
It derives its name from the Kaskaskia River. Floods have caused the town to be cut off by the river.
Kaskaskia began as a Native American village. In 1703 Jesuit missionaries established a mission there with the goal of converting the indigenous people to Catholicism. It also was used by the French as a post in the fur trade. In 1733 the French built Fort Kaskaskia at this site. It was destroyed by the British in 1763. The city fell to George Rogers Clark in 1778. It served as the capital of Illinois Territory from 1809 until statehood was gained in 1818. It then served as the capital of Illinois until 1820, when the capital moved to Vandalia. The village moved southward following the Great Flood of 1844. It was also at this time that the location of Kaskaskia became an island. The flood of 1881 destroyed all remnants of original.
In 1950 112 people lived in Kaskaskia. By 1970 the population had fallen to 79, and it continued its precipitous decline to only 33 in 1980. By 2000, with a mere 9 people, the place hardly existed at all.
Kaskaskia is located at (37.921395, -89.916467). According to the United States Census Bureau, the village has a total land area of 0.2809 km² (0.1085 sq mi, or 69.41 acres). None of the area is covered with water. However, the village comprises only a small part of Randolph County's land west of the Mississippi, known by the United States Census Bureau as Kaskaskia precinct, which includes the village. Kaskaskia precinct has a land area of 62.255 km² (24.037 sq mi) and a 2000 census population of 36 persons. In 1993 the Mississippi River almost completely flooded the island.
As of the census of 2000, there were 9 people, 4 households, and 3 families residing in the village. The population density was 83.0 people per square mile (31.6/km²). There were 5 housing units at an average density of 46.1/sq mi (17.6/km²). The racial makeup of the village was 77.78% White, 11.11% Pacific Islander, 11.11% from other races. Hispanic or Latino of any race were 22.22% of the population.
There were four households out of which none had children under the age of 18 living with them, two were married couples living together, one had a female householder with no husband present, and one was a non-family. One household was made up of individuals and one had someone living alone who was 65 years of age or older. The average household size was 2.25 and the average family size was 2.67.
In the village the population was spread out with 22.2% under the age of 18, 11.1% from 18 to 24, 11.1% from 25 to 44, 22.2% from 45 to 64, and 33.3% who were 65 years of age or older. The median age was 48 years. For every 100 females there were 28.6 males. For every five females age 18 and over, there were two males.