There is a whole book available on the origins and history of Ilkla Moor baht 'at by Arnold Kellett and it is still in print I believe.

It has been much published with the music since about the 1920s.

The tune is a hymn tune called 'Cranbrook' which would have been used in the West Riding as one of the many settings for 'While Shepherds' so it's very likely that the tune came to it via this route.