Joliet is a city in Will and Kendall counties in the U.S. state of Illinois, 35 miles (56 km) 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.

Will County is a county in the northeastern part of the state of Illinois. According to the 2020 census, it had a population of 696,355, an increase of 2.8% from 677,560 in 2010, making it Illinois's fourth-most populous county. The county seat is Joliet. Will County is one of the five collar counties of the Chicago–Naperville–Elgin, IL–IN–WI Metropolitan Statistical Area. The portion of Will County around Joliet uses area codes 815 and 779, while 630 and 331 are for far northern Will County and 708 is for central and eastern Will County.