You can cook deer tenderloin in much the same way as beef tenderloin, including country-fried or marinated and baked. Take care not to overcook deer; venison is a very lean meat, so it requires special attention during cooking.
For country-fried deer tenderloin, soak meat in 2 cups of milk for an hour. Mix together 2 cups all purpose flour, 1/2 teaspoon each salt and pepper, and 1 teaspoon each of garlic salt, lemon pepper and Mrs. Dash Extra Spicy Seasoning. Heat enough oil for frying over medium to medium-high heat. Remove meat from milk, and dredge in flour mixture. Fry slowly in hot oil, turning as needed. Remove and drain on a plate lined with paper towels.
To make a deer tenderloin bake, combine 2 cups soy sauce, 2 cups brown sugar, 2 teaspoons each of garlic powder and onion powder, 1/2 teaspoon hot sauce, 1/2 teaspoon salt, and 1/4 teaspoon pepper in large resealable bag. Add 2 pounds deer tenderloin, and refrigerate overnight. The next day, wrap approximately 15 strips of bacon around the tenderloin, covering it completely. Place in a 9-by-13 pan sprayed with cooking spray. Pour marinade over tenderloin. Bake in a preheated oven at 350 degrees for 25 to 55 minutes, depending on how rare you want the tenderloin. Switch the oven to broil to bring the bacon to a crispy finish. Let the meat stand for 10 minutes, then slice.