U.S. Federal Route 40 is the only east-west surface highway in Clark County. It runs through the central portion of the county. Clark County is the eastern most county in Illinois that U.S. Rt. 40 passes through. U.S. Rt. 40 passes through the following town in Clark County. Casey
Marshall U.S. Rt. 45 is multi-plexed in Clark County. Interstate 70, near State Line.
U.S. Rt. 40 intersects the following highways in Clark County. Illinois State Route 49, at Casey.