Place potatoes and onion in a 6-qt. slow cooker. In a small bowl, mix seasonings. Tuck wings under chicken; tie drumsticks together. Rub seasoning mixture over outside and inside of chicken. Place chicken over vegetables.
Cook, covered, on low 5-6 hours or until a thermometer inserted in thickest part of thigh reads 170°-175°. Remove chicken from slow cooker; tent with foil. Let stand 15 minutes before carving.
Transfer vegetables to a platter; keep warm. If desired, skim fat and thicken cooking juices for gravy. Serve with chicken.