There are two country capitals that I am aware of that have an apostrophe in them. One of them is St. George’s – the capital of Grenada. There are other capitals that have the quote mark – like Sa’ana or N’djamena or Nuku’alofa – but that is because there is a special way of pronouncing them locally. Why the posessive noun?

Finally, I have found the answer!

Turns out Grenada has seven parishes – St. Andrew, St. John, St. George, etc… In the early days, there would always be one important city – usually a port – in the parish where most business would be conducted. That city, usually, would be referred to as the “city of that particular parish”… in other words… St. George’s, St. John’s, or St. Andrew’s. Each parish in Grenada follows that rule.

Checked out Antigua and Barbuda. Sure enough… There is the St. John parish, which has the capital, called St. John’s!