Home Postcode finder SA Cape Douglas Cape Douglas postcode SA Cape Douglas is a locality in South Australia covered by postcode 5291. Postcode 5291 State or territory South Australia (SA) Region SA Outer Suburbs Add a free Cape Douglas business listing Be the first listing in Cape Douglas Common questionsWhat is the postcode for Cape Douglas?Cape Douglas, SA has the postcode 5291.What state is Cape Douglas in?Cape Douglas is in South Australia (SA).Does postcode 5291 cover more than one suburb?Yes. Postcode 5291 covers 34 localities, so the postcode alone does not identify Cape Douglas. Browse other postcodes in South Australia, or widen the search to every Australian postcode.