Its eastern terminus at Illinois Route 127 at a rural intersection west of Tamalco.

The rest of the road is generally rural and has 2 lanes.

In 1964, it was extended west again to Alton, replacing Illinois Route 159.

IL 143 was put on the new Madison Avenue alignment and routed on the Berm Highway, while IL 3 was put back on an older alignment through East Alton and the Homer Adams Parkway (later taking over the old IL 100 alignment north of Godfrey to Grafton), and IL 100 was put on then-unmarked River Road from Alton to Grafton.

The old alignment of IL 143 (Alton-Edwardsville Road) became unmarked.