It is not safe to cook a turkey in the oven overnight. Cooking a turkey overnight requires low temperatures over a long period of time. This can cause pathogens, such as salmonella, to grow, says LiveScience, which leads to food poisoning.
Turkeys should be cooked in the oven at a minimum temperature of 325 F. Use a meat thermometer to determine whether a turkey is done instead of relying on the exterior coloring as a guide. A turkey is safe to eat when the internal temperature reaches 165 F in the innermost thigh and thickest part of the breast, says the USDA.