Joliet is a city in Will and Kendall counties in the U.S. state of Illinois, 35 miles southwest of Chicago. It is the county seat of Will County. It ha…Joliet is a city in Will and Kendall counties in the U.S. state of Illinois, 35 miles southwest of Chicago. It is the county seat of Will County. It had a population of 150,362 at the 2020 census, making it the third-most populous city in Illinois.