A lot of John Denver fan clubs flourished and waned in the early years of John's career. The only one I belonged to was called "Sing With the Earth of the World Family of John Denver". It was first called just "Sing With the Earth", but the "World Family of John Denver" was a name that the John Denver Fan Clubs in existence at that time came up with during "Convention '78" - a convention of various JD Fan Clubs. Here is some information from those early "Sing with the Earth" fan Club Newsletters:
Another John Denver Fan Club I belonged to flourished on the Prodigy Online Service in 1993. Here is their January 1993 newsletter:
If you have any information on other older clubs, when they flourished, how many members they had, etc. please write to emily@sky.net I'd love to hear from you about those early days.