Joliet is a city in Will and Kendall counties in the U.S. state of Illinois, 30 miles (48 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's population at 150,495, which would make it the 3rd largest city in Illinois if accurate.