Collinsville, IL has a population of 24,855 and is the 1,744th largest city in the United States. The population density is 1,696 per sq mi which is 663% higher than the Illinois average and 1772% higher than the national average. The median age in Collinsville is 38 which is approximately 1% higher than the Illinois average of 37. In Collinsville, 55% of the population over 15 years of age are married, 97% speak English and 1% speak Spanish. 65% of Collinsville residents were born in Illinois, 32% were born out of state, 1% were born outside of the United States and 2% were foreign born.