Home Postcode finder QLD Grand Secret Grand Secret postcode QLD Grand Secret is a locality in Queensland covered by postcode 4820. Postcode 4820 State or territory Queensland (QLD) Region North QLD Add a free Grand Secret business listing Be the first listing in Grand Secret Common questionsWhat is the postcode for Grand Secret?Grand Secret, QLD has the postcode 4820.What state is Grand Secret in?Grand Secret is in Queensland (QLD).Does postcode 4820 cover more than one suburb?Yes. Postcode 4820 covers 21 localities, so the postcode alone does not identify Grand Secret. Browse other postcodes in Queensland, or widen the search to every Australian postcode.