Joliet, IL has a population of 147,515 and is the 177th largest city in the United States. The population density is 2,313 per sq mi which is 915% higher than the Illinois average and 2453% higher than the national average. The median age in Joliet is 33 which is approximately 11% lower than the Illinois average of 37. In Joliet, 53% of the population over 15 years of age are married, 74% speak English and 22% speak Spanish. 73% of Joliet residents were born in Illinois, 12% were born out of state, 1% were born outside of the United States and 14% were foreign born.