Home Postcodes by state WA 6125 Postcode 6125 6125 is the postcode for 3 localities in WA: Hopeland, Mardella and Serpentine. Localities with postcode 6125HopelandWAMardellaWASerpentineWA Postcode 6125 State or territory Western Australia (WA) Localities 3 Council area Serpentine-Jarrahdale Council area based on Australian Bureau of Statistics data (ASGS Edition 3), CC BY 4.0. Postcode 6124 · Postcode 6126