When Irish people went abroad they took stories fo the leprechaun with them and carried these around the world. Irish people mostly spoke English after the famine and the stories told abroad were interesting and funny, but did not have much depth.
Walt Disney became interested in leprechauns and even spent some time in Ireland looking for them. After this trip he made the movie Darby O'Gill and the Little People. Hollywood went on to make many more cartoons and films of the leprechaun including Finian's Rainbow (also a Broadway musical) written by EY Harburg (who also composed the lyrics for Somewhere Over the Rainbow). By now people all over the world came to see the leprechaun as a Hollywood character and somewhat removed from the old story telling history.
Leprechauns have been in Ireland for over a thousand years. Documents stretching back to the 8th century have described meetings with leprechauns. Even before this the Irish people were telling stories around their firesides, enchanting and delighting their audiences. There are many stories about the leprechaun and otherworld creatures in Irish folklore. Leprechauns exist in a world of the imagination and the unknown. To many people this world existed right outside their door and as the evenings grew dark, the land came alive with the people of the other world.