IL Route 4 is an important road in St. Clair and Madison counties as it connects many suburbs and exurbs on the eastern edge of St. Louis, including Mascoutah, Lebanon, Troy, Highland, Edwardsville, Hamel, Staunton, Benld, and Gillespie.

From Carlinville northwards the route is important since it connects many medium-sized rural towns and bedroom communities in Macoupin and Sangamon counties, such as Girard, Virden, Auburn, and Chatham, with Springfield.

It completes the western loop around the city, and is a divided four-lane highway that serves the major commercial area centered around the intersection of Veterans Parkway and Wabash Avenue, which includes White Oaks Mall.

In 1926, a new alignment for Route 4 was opened between Joliet and Lyons, on the north side of the Des Plaines River.

It was added in 1998 as structure #98000979 and consists of two c.1920 bridges over Little Panther Creek and portions of Curran and Snell roads.