Knollwood, IL has a population of 1,729 and is the 11,889th largest city in the United States. The population density is 2,864 per sq mi which is 1188% higher than the Illinois average and 3061% higher than the national average. The median age in Knollwood is 40 which is approximately 7% higher than the Illinois average of 37. In Knollwood, 54% of the population over 15 years of age are married, 75% speak English and 16% speak Spanish. 67% of Knollwood residents were born in Illinois, 18% were born out of state, 2% were born outside of the United States and 13% were foreign born.