U.S. Federal Route 67 is the main north-south highway in Warren County. It is a four-lane highway from the Mc Donough/Warren County Line to near Monmouth. North of Monmouth it is a two lane highway to the Warren/Mercer County Line. U.S. Rt. 67 passes through the following town in Warren County. Monmouth
U.S. Rt. 67 is multi-plexed in Warren County. Illinois State Route 110, from the Mc Donough/Warren County Line to Monmouth.