Joliet is a city in Will and Kendall Counties in the U.S. state of Illinois, located 40 miles (64km) southwest of Chicago. It is the county seat of Will County. It continues to be Illinois' fastest growing city and one of the fastest growing in the United States. When Joliet was first planned in the early 1830s, it was still in Cook County. In 1836, it became the county seat of the new Will County.