Where is the thermostat on 4.0 jeep motor?

The thermostat on this vehicle is mounted in the cylinder head. More precisely, follow the upper radiator hose back toward the engine and remove the hose where it connects to the engine - the thermostat is the circular object beneath the hose outlet flange. To make reinstallation easier I would use the screw-tighten hose clamps rather than the factory clamps which are a bear to reinstall properly.