Home Postcodes by state SA 5421 Postcode 5421 5421 is the postcode for 2 localities in SA: Franklyn and Terowie. Localities with postcode 5421FranklynSATerowieSA Postcode 5421 State or territory South Australia (SA) Localities 2 Council area Goyder Council area based on Australian Bureau of Statistics data (ASGS Edition 3), CC BY 4.0. Postcode 5420 · Postcode 5422