Home Postcodes by state SA 5451 Postcode 5451 5451 is the postcode for 2 localities in SA: Auburn and Undalya. Localities with postcode 5451AuburnSAUndalyaSA Postcode 5451 State or territory South Australia (SA) Localities 2 Council area Clare and Gilbert Valleys Council area based on Australian Bureau of Statistics data (ASGS Edition 3), CC BY 4.0. Postcode 5440 · Postcode 5452