Joliet is a city in Kendall and Will counties in the U.S. state of Illinois, 30 miles southwest of Chicago. It is the county seat of Will County and part of southwest Chicagoland. At the 2010 census, the city was the fourth largest in Illinois, with a population of 147,433. A special census in 2016 put Joliet's population at 149,395, making it the 3rd largest city in Illinois.