New Lenox, IL has a population of 25,347 and is the 1,701st largest city in the United States. The population density is 1,629 per sq mi which is 633% higher than the Illinois average and 1698% higher than the national average. The median age in New Lenox is 37 which is approximately 1% lower than the Illinois average of 37. In New Lenox, 64% of the population over 15 years of age are married, 95% speak English and 2% speak Spanish. 87% of New Lenox residents were born in Illinois, 10% were born out of state, 0% were born outside of the United States and 2% were foreign born.