Melt butter in large skillet on medium heat. Add celery and onion; cook and stir until softened, about 5 minutes. Add sausage; cook and stir until no longer pink, about 5 minutes.
Spray inside of slow cooker with no stick cooking spray. Add stock and herbs; stir to blend. Stir in bread cubes and sausage-vegetable mixture. Cover.
Cook 45 minutes on high. Uncover and stir. Cook, uncovered, 30 minutes longer.