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. At the 2010 census, the city was the fourth-largest in Illinois, with a population of 147,433. A population estimate in 2019 put Joliet's population at 147,344, which would make it the fourth-largest city in Illinois if accurate.
In 1673, Louis Jolliet, along with Father Jacques Marquette, paddled up the Des Plaines River and camped on a huge mound, a few miles south of present-day Joliet. Maps from Jolliet's exploration of the area placed a large hill or mound on what is now the southwest corner of the city, since no point is farther southwest. That hill was named Mound Jolliet. The spot was mined by early settlers and is now a depression.
In 1833, following the Black Hawk War, Charles Reed built a cabin along the west side of the Des Plaines River. Across the river in 1834, James B. Campbell, treasurer of the canal commissioners, laid out the village of "Juliet", named after his daughter. Just before the economic depression of 1837, Juliet incorporated as a village, but to cut tax expenses, Juliet residents soon petitioned the state to rescind that incorporation.