Note that the text quoted above was noted by Butterworth from Mrs Whiting of Newport, Monmouthshire, in April 1908.

The song was printed as 'Willy-O!' on Irish broadsides in the later part of the 19th century, and seems to have originated there; for several examples, see  Bodleian Library Broadside Ballads:

Willy O!

There is some confusion about how it ought to be classified. Some examples are loosely categorised as a member of the night-visiting complex that also includes 'The Grey Cock' ( Child 248 / Roud number 179 ), though the songs are separate and made on similar lines rather than directly related, verses from 'Willy' have at times wandered into examples of 'The Grey Cock', leading people to believe (probably wrongly) that the latter was originally a revenant song that has in most cases lost its supernatural element, rather than a night-visiting song which has occasionally picked up supernatural elements from elsewhere.

The boundaries are frequently blurred: the well-known 'Grey Cock' that Cecilia Costello sang, for example, borrowed three verses from 'Willie-O'.

Other examples are classed under Child 77 / Roud 50: 'Sweet William's Ghost', and it seems likely that the Irish broadside was partly based on that song.

There is a fair bit of related material here in the Forum; see in particular the following, which in turn contain links to more:

Lyr Add: WILLY O!

hughie jones' sweet william's ghost

Help: Bay of Biscay - My Willie Sails

In the DT:

GHOST OF WILLIE-O  (text only; no source named).