Home Postcode finder WA Cossack Cossack postcode WA Cossack is a locality in Western Australia covered by postcode 6720. Postcode 6720 State or territory Western Australia (WA) Region North West Suburbs Add a free Cossack business listing Be the first listing in Cossack Common questionsWhat is the postcode for Cossack?Cossack, WA has the postcode 6720.What state is Cossack in?Cossack is in Western Australia (WA).Does postcode 6720 cover more than one suburb?Yes. Postcode 6720 covers 3 localities, so the postcode alone does not identify Cossack. Browse other postcodes in Western Australia, or widen the search to every Australian postcode.