Where is the thermostat on a 2001 ford taurus sel located

The thermostat on most internal combustion engines controls the flow of coolant to the radiator and this is fed into the top tank of the radiator. The bottom hose is normally at the inlet to the coolant pump.
Vehicles with AC will have two radiators, and even some, a third for transmission or oil cooling but the largest of them will be the one handling engine cooling.
Locate the topmost hose of the radiator and simply follow it back toward the engine and it is normally connected to a dome-like fitting, under which you will find the thermostat.
If you are experiencing overheating though, it may not be a failed thermostat; this can be caused by a radiator blocked with debris, an internally collapsed hose and worst case, a failing head-gasket. The latter can fail in several places and overheating is often caused by the failure of it between coolant channels and one or more of the cylinders. This allows passage of hot combustion gases directly into the coolant flow.
Check the following: the overflow bottle for traces of oil contamination and possible odor of exhaust fumes, the oil dipstick for a milky deposit and when the engine is running, the overflow bottle for bubbles.

The thermostat is located under a housing bolted to the engine. To locate the housing, follow the large hose coming out of the top of the radiator to the engine.