Boil the red potatoes until fork-tender, then let them cool before dicing.
In a large mixing bowl, combine the diced potatoes, chopped red onion, celery, and hard-boiled eggs.
In a separate bowl, mix mayonnaise, Dijon mustard, salt, and pepper to create the dressing.
Gently fold the dressing into the potato mixture until well-coated.
Add fresh dill and stir gently to incorporate the flavors.
Adjust salt and pepper to taste.
Refrigerate for at least 2 hours to allow flavors to meld.