Joliet (/ ˈ dʒ oʊ l i ɛ t, dʒ oʊ l i ˈ ɛ t /) is a city in Will and Kendall counties in the U.S. state of Illinois, 25 miles (40 km) southwest of Chicago.It is the county seat of Will County and a major part of the southwest Chicago metropolitan area. At the 2010 census, the city was the fourth largest in Illinois, with a population of 147,433. A population estimate in 2018 put Joliet ...