https://www.cnet.com/news/facebook-data-of-over-300000-australians-hit-in-data-scandal/

Facebook on Thursday revealed the extent of the data sharing and said it estimates just over 300,000 Australians were implicated. That's around 1.2 percent of the country's population. 

From Facebook's graph, it appears Australia was the 10th hardest hit country. With 70.5 million compromised accounts, the US sits at the top. It makes sense, since the data was used to inform Facebook advertisements for the Trump campaign. You can see the full graph below.