Home Postcode finder SA Franklyn Franklyn postcode SA Franklyn is a locality in South Australia covered by postcode 5421. Postcode 5421 State or territory South Australia (SA) Region SA Outer Suburbs Add a free Franklyn business listing Be the first listing in Franklyn Common questionsWhat is the postcode for Franklyn?Franklyn, SA has the postcode 5421.What state is Franklyn in?Franklyn is in South Australia (SA).Does postcode 5421 cover more than one suburb?Yes. Postcode 5421 covers 2 localities, so the postcode alone does not identify Franklyn. Browse other postcodes in South Australia, or widen the search to every Australian postcode.