Is there a switch that will keep 2001 Chevy Malibu from starting if the gas tank is overfilled and so where it?

No, there isn't a standard factory-installed switch in a 2001 Chevy Malibu (or any other car) that prevents starting due to an overfilled gas tank. Cars don't have this feature. Overfilling is prevented by the design of the gas tank and filler neck – a vent prevents overfilling and causes the fuel pump to shut down when the tank is full. While a poorly designed or damaged filler system might allow significant overfilling, there's no safety interlock that stops the engine from starting.