I wrote here about the origins of the word "libertarian", placing its adoption by Classical Liberals in the US to the 1970s. This is incorrect. In an introduction quoted in The Life and Works of Thomas Paine, Thomas Edison wrote:
Paine was too great a libertarian to be satisfied with the independence of America, so he went abroad and sought freedom for England with his "Rights of Man."The book was based on two earlier collections, and was published in the 1940s but Edison died in 1931 so his introduction must pre-date this, and probably came from one of the earlier volumes, probably in the 1920s.
I'm starting to suspect this usage will prove to have begun even earlier.