Home Postcodes by state WA 6720 Postcode 6720 6720 is the postcode for 3 localities in WA: Cossack, Point Samson and Wickham. Localities with postcode 6720CossackWAPoint SamsonWAWickhamWA Postcode 6720 State or territory Western Australia (WA) Localities 3 Council area Karratha Council area based on Australian Bureau of Statistics data (ASGS Edition 3), CC BY 4.0. Postcode 6718 · Postcode 6721