There's a slight difference.
1) Have you ever heard of Georgia? This means your asking if the other person knows what Georgia is, in other words that there is a country called Georgia. Its existence.
2) Have you (ever) heard about Georgia? This assumes that the person knows that there is a country called Georgia. The question is asking if they heard the news or some other story about Georgia. Note: the word "ever" would not be used in this meaning of the sentence.
Have you ever heard about Georgia? If you include the word "ever", then using "about" is more like answer #1. However, using "of" is still better in that case.