Algonquin, IL has a population of 30,413 and is the 1,399th largest city in the United States. The population density is 2,482 per sq mi which is 1017% higher than the Illinois average and 2640% higher than the national average. The median age in Algonquin is 39 which is approximately 5% higher than the Illinois average of 37. In Algonquin, 65% of the population over 15 years of age are married, 81% speak English and 5% speak Spanish. 68% of Algonquin residents were born in Illinois, 18% were born out of state, 1% were born outside of the United States and 13% were foreign born.