In the U.S. state of Illinois, U.S. Route 34 is an east–west highway that runs from the Iowa state line at Gulfport, west of Galesburg, to Illinois Route 43 and Historic U.S. Route 66 at Harlem Avenue in Berwyn. The entire highway in Illinois is named the "Walter Payton Memorial Highway". The highway is 211.37 miles (340.17 km) long within the state.

The bridge into Iowa over the Mississippi River is called the Great River Bridge.

Between Monmouth and Galesburg, the highway is up to interstate standards with exits at Main Street, Henderson Street, and Seminary Street in Galesburg.

In 1934, US 34 absorbed what had been the last remaining section of US 32.

US 34 formerly overlapped US 66 all the way to its endpoint in downtown Chicago, but was truncated to its intersection with US 66 and IL 43 in Berwyn in 1970. When US 66 was subsequently eliminated, the endpoint of US 34 was left at that location—the intersection of Ogden and Harlem Avenues in Berwyn. Due to the elimination of US 66, it is one of the few US Numbered Highways that ends at a state highway. With the re-signing of much of Historic US 66, the history of US 34's eastern endpoint is becoming much more clear.

The now cancelled Prairie Parkway limited access highway would have had an interchange with U.S. Route 34, between Needham Road and Waubonsee Drive in the city of Plano.