To find it, you'll likely need to:
* Consult a repair manual specific to your Cavalier's year and engine: This will give you diagrams and precise locations. A Haynes or Chilton manual would be a good resource.
* Look for a housing with a hose leading to the radiator and another to the engine block: This housing will contain the thermostat.
* Be prepared to potentially remove some components for better visibility: This might include parts of the air intake system or other accessories.
Without knowing the exact year and engine of your Cavalier, a more precise location can't be given. The location can vary slightly between model years and engine types.