Illinois Route 75 is an east–west state road in north-central Illinois. It runs from downtown Freeport at Illinois Route 26 to WIS 67 at the Wisconsin state line southeast of Beloit, Wisconsin. This is a distance of 41.64 miles (67.01 km).

Illinois 75 is the main route between Freeport and Beloit, and serves numerous rural areas along this alignment. It has two lanes and is an undivided surface street for its entire length, except at the interchange with U.S. Route 20 and the section east of Illinois Route 2.

SBI Route 75 originally ran from Freeport to Rockton. It was extended in 1960 along Illinois Route 2 to U.S. Route 51 in South Beloit.