It is an east–west highway that runs from Illinois Route 48 in Decatur to Interstate 72 near Monticello.

Roads such as IL-105 carry corn and soybeans to the refineries of Decatur for the manufacture of commodities such as soybean oil and corn syrup.

Rural towns along Illinois Route 105 include Bement and Cerro Gordo.

The highway also runs past the Bryant Cottage State Historic Site.

In 1945, the number was reused on former Illinois Route 47 north of Decatur.