Illinois Route 159 is a north–south state route in southwestern Illinois. Its southern terminus is at Illinois Route 3 and Illinois Route 154 in Red Bud and its northern terminus at Illinois Route 16 in Royal Lakes. This is a distance of 64.90 miles (104.45 km).

Illinois Route 16 is an east–west highway in central Illinois. Its western terminus is at the Joe Page Bridge over the Illinois River in Hardin, while its eastern terminus is at Paris at Illinois Route 1 and U.S. Route 150, with Illinois Route 133. This is a distance of 174.66 miles (281.09 km).