Home Postcode finder SA Mount Observation Mount Observation postcode SA Mount Observation is a locality in South Australia covered by postcode 5255. Postcode 5255 State or territory South Australia (SA) Region Sa Subs Near 2 Add a free Mount Observation business listing Be the first listing in Mount Observation Common questionsWhat is the postcode for Mount Observation?Mount Observation, SA has the postcode 5255.What state is Mount Observation in?Mount Observation is in South Australia (SA).Does postcode 5255 cover more than one suburb?Yes. Postcode 5255 covers 19 localities, so the postcode alone does not identify Mount Observation. Browse other postcodes in South Australia, or widen the search to every Australian postcode.