Place ground beef in a large skillet over medium heat, and cook until brown, breaking up the meat as it cooks, about 15 minutes. Drain excess grease.
Place the cooked meat, onion, garlic, celery, salt, black pepper, cider vinegar, mustard, brown sugar, and ketchup into a slow cooker, and stir to combine. Set the cooker on Low, and cook for 6 to 8 hours.
