Home Postcode finder SA St Marys St Marys postcode SA St Marys is a locality in South Australia covered by postcode 5042. Postcode 5042 State or territory South Australia (SA) Region Sa Subs Near 1 Add a free St Marys business listing More business listings in St Marys Businesses in St MarysAdrian Brien Ford1305 South Road · (08) 8374 5444Adrian Brien Ford1305 South Road · 0883745444Adrian Brien Ford1305 South Road · (08) 8374 5444 Common questionsWhat is the postcode for St Marys?St Marys, SA has the postcode 5042.What state is St Marys in?St Marys is in South Australia (SA).Does postcode 5042 cover more than one suburb?Yes. Postcode 5042 covers 5 localities, so the postcode alone does not identify St Marys. Browse other postcodes in South Australia, or widen the search to every Australian postcode.