Illinois Route 15 (IL 15) is a 149.64-mile-long (240.82 km) east–west highway in southern Illinois with its western terminus at Illinois Route 3, U.S. Route 40, I-55, and I-64, and its eastern terminus at Wabash River at the Illinois/Indiana Border where it meets State Road 64.

Vernon, IL 15 was part of US 460.

The section from Nashville to St. Libory was once IL 110, but this was back in the 1940s before US 460 was signed.

[1] The current route was determined in 1967.

[2] In 2011, the old Parker truss bridge crossing the Wabash River was replaced by a beam bridge.