In a 3-1/2- or 4-quart slow cooker combine mushrooms, celery, onion, dill, and pepper. Place chicken thighs on top of mushroom mixture. In a small bowl combine soup and chicken broth. Pour over chicken.
Cover and cook on low-heat setting for 5 to 6 hours or on high-heat setting for 2-1/2 to 3 hours.
If using low-heat setting, turn slow cooker to high-heat setting. Stir uncooked rice into the mushroom mixture. Cover and cook for 10 minutes more. Makes 4 servings.