Missouri State Route 340 runs east-west in the western areas of St. Louis County. In Chesterfield it turns into a north-south highway. MO St Rt 340 passes through the following towns in St. Louis County. Ellisville Clarkson Valley Ballwin Chesterfield Creve Coeur
Olivette University City MO St Rt 340 is not multi-plexed in St. Louis County. MO St Rt 340 intersects the following highways in St. Louis County. Missouri State Route 100, at Ellisville. Missouri Secondary State Route HH, at Ellisville. Interstate 64, at Chesterfield. U.S. Rt. 40, at Chesterfield. U.S. Rt. 61, at Chesterfield. Missouri State Route 141, near Chesterfield. Interstate 270, at Creve Coeur.
