Cook bacon in a large skillet over medium heat, turning occasionally, until crispy, about 8 minutes. Transfer to a paper-towel-lined plate to cool, reserving the drippings. Crumble the cooled bacon and refrigerate until ready to serve.

Discard all but 2 tablespoons of the drippings. Off the heat, add vinegar to the pan. When it stops steaming, scrape up any browned bits. Whisk mustard and flour in a small bowl; add the vinegar mixture and whisk until combined. Whisk in salt and pepper.

Combine potatoes, celery, onion and the dressing in a 5- to 6-quart slow cooker; stir until the vegetables are well coated. Cover and cook on Low for 5 hours.

To serve, stir in dill and the bacon.