U.S. Federal Route 40 is an east-west highway in Cooper County. It enters the county at the Boonville-Missouri River Bridge. Southwest of Boonville U.S. Rt. 40 joins Interstate 70. U.S. Rt. 40 passes through the following town in Cooper County. Boonville
WB U.S. Rt. 40; SB MO St Rt 5/87 in Boonville. A junction marker on WB BUSN Loop I-70/NB MO St Rt 87. WB BUSN Loop I-70/U.S. Rt. 40; SB MO St Rt 5 west of Boonville. WB BUSN Loop I-70/U.S. Rt. 40; SB MO St Rt 5 near I-70. A BGS on EB I-70/U.S. Rt. 40. EB I-70/U.S. Rt. 40 east of the Cooper/Saline County Line.