From above: Derry Air at Contemplator

However, if you search HERE at the Mudcat (using the handy Lyric Search box at the top of the page, you will get most of what can be found on the songs/tune of Danny Boy/Londonderry Air/Derry Air.

Michael Robinson's site has about as complete a history of the song, Danny Boy as you're likely to find.

But here at the Mudcat we've dealt with a lot of theory and such behind some of the other songs and such of the older tune. Essentially, we don't really know the oldest song but there are a few oldies available.