Preheat oven to 350 degrees.
Remove giblets and rinse chicken. Place the chicken in a roasting pan and season inside and out with salt and pepper. Sprinkle the onion powder inside and outside the chicken. Place 3 tablespoons of butter in the cavity of the chicken. Arrange pieces of the remaining butter around the outside of the chicken. Cut the celery into 3 or 4 pieces and place inside the cavity of the chicken.
Bake uncovered approximately 1 hour and 15 minutes in a preheated oven, to a minimum internal temperature of 180 degrees F. Remove from heat and baste with melted butter and drippings. Cover with aluminum foil and allow to rest 20-30 minutes before serving.