By the time of the 1740s, Cahokia had become a large area for trading Indian goods and furs. In the city of Cahokia, there were about 3,000 inhabitants, 24 stores, and a thriving business district. Also in the nearby town of Kaskaskia, it had become the region’s leading shipping port and the Fort de Chartres had become a military and governmental command center. The area of land between the two cities had become a major area for farming settlers, whose main crop was wheat. As the area expanded and expanded, the relationship between the settlers and the Indians continued to be peaceful.
In the following years, Cahokia suffered very much, mainly from the French loss in the French and Indian War in 1763. The French were forced to give large parts of the Illinois County to Great Britain. Many Cahokians fled in fear of the British, some went to areas like St. Genevieve. Some of these relocated Cahokians helped to build the city of St. Louis in 1764.
In 1778, during the American Revolutionary War, George Rogers Clark set up a court in Cahokia, because in earlier years Cahokia was just an independent city state. Cahokia officially became part of the United States on July 5, 1778. Soon after that, the 105 Cahokia "heads of household" pledged loyalty to the Continental Congress of the United States. Later, Cahokia was named the county seat of St. Clair County. The Cahokian Courthouse then acted as a United States territorial courthouse and a major political center for the next 24 years. Then later in 1801 when St. Clair County was enlarged, Henry Harrison named the Cahokia Courthouse the legal and governmental center of a sizeable area extending to the Canadian border. By 1814, though, St. Clair County had decreased to its current size and the county seat was moved to Belleville, Illinois.
According to the United States Census Bureau, the village has a total area of 10.0 square miles (25.8 km²), of which, 9.6 square miles (24.9 km²) of it is land and 0.4 square miles (1.0 km²) of it (3.71%) is water.
There were 5,693 households out of which 41.2% had children under the age of 18 living with them, 43.2% were married couples living together, 25.7% had a female householder with no husband present, and 25.3% were non-families. 20.9% of all households were made up of individuals and 8.6% had someone living alone who was 65 years of age or older. The average household size was 2.84 and the average family size was 3.27.
In the village, the population was spread out with 33.4% under the age of 18, 8.7% from 18 to 24, 29.4% from 25 to 44, 16.9% from 45 to 64, and 11.6% who were 65 years of age or older. The median age was 31 years. For every 100 females there were 88.7 males. For every 100 females age 18 and over, there were 82.5 males.
The median income for a household in the village was $31,001, and the median income for a family was $35,582. Males had a median income of $31,806 versus $22,429 for females. The per capita income for the village was $14,545. About 22.8% of families and 24.9% of the population were below the poverty line, including 37.0% of those under age 18 and 5.3% of those age 65 or over.