Illinois State Route 23 runs north-south in Western Mc Henry County. It runs from the De Kalb/Mc Henry County Line, near Riley, to U.S. Rt. 14, near Harvard. IL St Rt 23 passes through the following town in Mc Henry County. Marengo IL St Rt 23 is not multi-plexed in Mc Henry County. IL St Rt 23 crosses the following highways in Mc Henry County. Interstate 90, (Addams Tollway) near Riley. (NO INTERCHANGE) U.S. Rt. 20, at Marengo. Illinois State Route 176, at Marengo. U.S. Rt. 14, near Richmond.