It runs east from near Beecher City to meet Illinois Route 32 in Shumway.

Two miles north of Newton it branches off and travels east through Oblong and then to Robinson.

Illinois 33 continues south, parallel to the Wabash River and beneath U.S. Route 50.

[2] Illinois 33 then travels west (along the old alignment of U.S. 50) and then back north to meet its terminus at a full interchange with U.S. 50.

In 1937,[4] 1941 and 1948, extensions were made east to Palestine, west to Beecher City, and then south to U.S. 50 to complete the route.