U.S. Federal Route 18 is a east-west highway across Northern Clayton County. This runs from the Clayton/Allamakee County Line, near Postville to the Iowa/Wisconsin State Line, near Marquette. U.S. Rt. 18 passes through the following towns in Clayton County. Luana Monona Froelich Giard Marquette
U.S. Rt. 18 is multi-plexed in Clayton County. U.S. Rt. 52, from the Allamakee/Clayton County Line to near Froelich. U.S. Rt. 18 intersects the following highways in Clayton County. U.S. Rt. 52, near Froelich. BUSN U.S. Rt. 18, near Mc Gregor. Iowa State Route 76, near Mc Gregor. BUSN U.S. Rt. 18, at Marquette. Iowa State Route 76, at Marquette.