Cook the elbow macaroni according to the package instructions. Drain and let cool.
In a large bowl, combine the shrimp, cooked macaroni, celery, and red onion.
In a separate bowl, whisk together the mayonnaise, lemon juice, Dijon mustard, salt, and pepper.
Pour the dressing over the salad ingredients and toss to combine.
Refrigerate for at least 1 hour before serving to allow the flavors to meld.
Garnish with fresh dill before serving.