Home Postcodes by state WA 6427 Postcode 6427 6427 is the postcode for Koolyanobbing, WA. Localities with postcode 6427KoolyanobbingWA Postcode 6427 State or territory Western Australia (WA) Localities 1 Council area Yilgarn Council area based on Australian Bureau of Statistics data (ASGS Edition 3), CC BY 4.0. Postcode 6426 · Postcode 6428