[4] Illinois 133 is a two-lane undivided surface state highway for its entire length.

It overlaps Illinois 16 when both roads terminate at U.S. 150/Illinois 1 in Paris.

The Illinois 16/133 combination runs west.

SBI Route 133 was the same as Illinois 133 is today, though the eastern portion of the road from Redmon to Paris was not completed until 1942.

In 1953 it was extended west to Decatur along Illinois 32; this was rescinded in 1972.