https://archive.org/details/bim_early-english-books-tract-su...
The freedoms in that instance are freedom of religion, and democracy. (Democracy, the franchise, was limited to about 10% of men, under rules that varied locally from "you have to own a house" to "you have to own the entire region".)
But here the concept is again in ancient times:
https://archive.org/details/BiblicalCollectionPrintedBetween...
This is (a translation of) Josephus, writing in the first century about a speech by a Roman senator from the time when Claudius was put on the throne, with lines like "our natural freedom", "breath of liberty", and "the Liberty of former Times, that was dead and gone before ever I came into the World ..." I can't work out what that freedom was all about - Claudius came after Caligula, though, so you can make a good guess - but evidently this kind of concept is much older than the United States.
I also found the phrase "it's a free country" in Uncle Tom's Cabin, where the freedom in question is the freedom to control slaves.
So the concept is:
• Not modern,
• Not well defined,
• But not meaningless, either.