Add the carrots, celery and onion to the bottom of the crockpot and spread them out into an even layer.
Pat the chicken dry with paper towels and lightly coat the outside with olive oil. In a small bowl, stir together the salt, pepper, garlic powder, onion powder, paprika, poultry seasoning, thyme and rosemary. Rub the seasoning mixture all over the chicken until it is evenly coated. Place the seasoned chicken on top of the vegetables in the crockpot.
Add the pats of butter evenly over the top of the chicken. Cover and cook on LOW for 7–8 hours, or until the chicken is cooked through and reaches an internal temperature of at least 165°F.
Carefully remove the chicken from the crockpot and let it rest for about 10 minutes before carving. Serve with the cooked vegetables and some of the juices from the bottom of the crockpot, if desired.