Cahokia, IL has a population of 14,574 and is the 2,899th largest city in the United States. The population density is 1,493 per sq mi which is 572% higher than the Illinois average and 1548% higher than the national average. The median age in Cahokia is 35 which is approximately 6% lower than the Illinois average of 37. In Cahokia, 37% of the population over 15 years of age are married, 97% speak English and 2% speak Spanish. 63% of Cahokia residents were born in Illinois, 36% were born out of state, 0% were born outside of the United States and 1% were foreign born.