Preheat oven to 350°F. Let chicken sit at room temperature for roughly 30 minutes.
Cut butter into 1/2 tablespoon-sized chunks. Chop each celery stalk into 3 pieces of equal length.
Thoroughly drain chicken and remove giblets, discarding (or separately cooking) the livers. Place the chicken in a roasting pan alongside the giblets.
Place celery in the chicken cavity, followed by 3 tablespoons of the butter. Distribute the remaining butter evenly around the chicken in the bottom of the pan.
Generously season the outside and inside of the chicken with salt, pepper, and onion powder.
Bake chicken uncovered for about 1 hour and 15 minutes, or until a thermometer reads 165 degrees when inserted at the thickest part of the thigh.
Remove from oven and baste with drippings. Cover with foil and rest for 30 minutes before carving and serving.