Home Postcodes by state WA 6121 Postcode 6121 6121 is the postcode for 2 localities in WA: Oakford and Oldbury. Localities with postcode 6121OakfordWAOldburyWA Postcode 6121 State or territory Western Australia (WA) Localities 2 Council area Serpentine-Jarrahdale Council area based on Australian Bureau of Statistics data (ASGS Edition 3), CC BY 4.0. Postcode 6112 · Postcode 6122