Roughly chop the imitation crab into bite-sized pieces. If using larger cooked shrimp, cut them into smaller pieces if desired.
In a large mixing bowl, whisk together the mayonnaise, lemon juice, Old Bay seasoning, salt, and black pepper until smooth.
Stir in the finely diced celery, red onion, and chopped fresh dill until evenly combined.
Add the imitation crab and cooked shrimp to the bowl. Gently fold everything together until the seafood is coated in the creamy dressing.
Cover the bowl and refrigerate for at least 1 hour to allow the flavors to blend.
Give the salad a gentle stir before serving. Enjoy it chilled with crackers, croissants, sandwich rolls, or a bed of fresh greens.