Glen Carbon, IL has a population of 12,782 and is the 3,252nd largest city in the United States. The population density is 1,268 per sq mi which is 470% higher than the Illinois average and 1300% higher than the national average. The median age in Glen Carbon is 38 which is approximately 1% higher than the Illinois average of 37. In Glen Carbon, 64% of the population over 15 years of age are married, 96% speak English and 2% speak Spanish. 61% of Glen Carbon residents were born in Illinois, 35% were born out of state, 1% were born outside of the United States and 3% were foreign born.