Illinois Route 78 is a major north–south highway in western Illinois. It runs from Illinois Route 104 northwest of Jacksonville north to Highway 78 at the Wisconsin state line north of Warren. This is a distance of 215.51 miles (346.83 km).

Illinois Route 104 is a state highway in central and western Illinois. It extends from Illinois Route 29 near Taylorville, west over the Illinois River at Meredosia to its western terminus in downtown Quincy. This is a distance of 125.91 miles (202.63 km).