Home Postcode finder SA Thomas Plain Thomas Plain postcode SA Thomas Plain is a locality in South Australia covered by postcode 5554. Postcode 5554 State or territory South Australia (SA) Region Sa Subs Near 1 Add a free Thomas Plain business listing Be the first listing in Thomas Plain Common questionsWhat is the postcode for Thomas Plain?Thomas Plain, SA has the postcode 5554.What state is Thomas Plain in?Thomas Plain is in South Australia (SA).Does postcode 5554 cover more than one suburb?Yes. Postcode 5554 covers 10 localities, so the postcode alone does not identify Thomas Plain. Browse other postcodes in South Australia, or widen the search to every Australian postcode.