Home Postcode finder QLD Mount St John Mount St John postcode QLD Mount St John is a locality in Queensland covered by postcode 4818. Postcode 4818 State or territory Queensland (QLD) Region North QLD Add a free Mount St John business listing Be the first listing in Mount St John Common questionsWhat is the postcode for Mount St John?Mount St John, QLD has the postcode 4818.What state is Mount St John in?Mount St John is in Queensland (QLD).Does postcode 4818 cover more than one suburb?Yes. Postcode 4818 covers 18 localities, so the postcode alone does not identify Mount St John. Browse other postcodes in Queensland, or widen the search to every Australian postcode.