Lemont, IL has a population of 16,587 and is the 2,577th largest city in the United States. The population density is 2,048 per sq mi which is 821% higher than the Illinois average and 2160% higher than the national average. The median age in Lemont is 43 which is approximately 14% higher than the Illinois average of 37. In Lemont, 65% of the population over 15 years of age are married, 79% speak English and 3% speak Spanish. 73% of Lemont residents were born in Illinois, 12% were born out of state, 1% were born outside of the United States and 14% were foreign born.