J'habite à Perth au Australia

Bonjour Scott ! "J'habite à Perth" is correct if you're talking about a city, however to say "in Australia", you'll say: "en Australie". See the related lesson: https://french.kwiziq.com/revision/grammar/use-en-with-feminine-countries-and-aux-with-masculine-countries-to-say-in-or-to-prepositions À bientôt !