Charleston, IL has a population of 21,257 and is the 2,045th largest city in the United States. The population density is 2,459 per sq mi which is 1006% higher than the Illinois average and 2614% higher than the national average. The median age in Charleston is 25 which is approximately 34% lower than the Illinois average of 37. In Charleston, 36% of the population over 15 years of age are married, 93% speak English and 2% speak Spanish. 77% of Charleston residents were born in Illinois, 19% were born out of state, 0% were born outside of the United States and 4% were foreign born.