Clarendon Hills, IL has a population of 8,641 and is the 4,404th largest city in the United States. The population density is 4,812 per sq mi which is 2065% higher than the Illinois average and 5212% higher than the national average. The median age in Clarendon Hills is 39 which is approximately 5% higher than the Illinois average of 37. In Clarendon Hills, 65% of the population over 15 years of age are married, 88% speak English and 4% speak Spanish. 64% of Clarendon Hills residents were born in Illinois, 25% were born out of state, 1% were born outside of the United States and 10% were foreign born.