The current owners Warner/Chappell acquired the copyright originally filed in 1935 in 1988. The Judge George King ruled that the original copyright was only granted for a specific arrangements of the music not of the song itself.
The ditty was written by two Kentucky sisters in 1893.
Despite this ruling you still need to exercise considerable care when it comes to producing this song as the song stil remains a protected work under the laws of copyright.Â
Copy of the Judgment can be found here.Â