Home Postcode finder SA Millbrook Millbrook postcode SA Millbrook is a locality in South Australia covered by postcode 5231. Postcode 5231 State or territory South Australia (SA) Region Sa Subs Near 2 Add a free Millbrook business listing Be the first listing in Millbrook Common questionsWhat is the postcode for Millbrook?Millbrook, SA has the postcode 5231.What state is Millbrook in?Millbrook is in South Australia (SA).Does postcode 5231 cover more than one suburb?Yes. Postcode 5231 covers 3 localities, so the postcode alone does not identify Millbrook. Browse other postcodes in South Australia, or widen the search to every Australian postcode.