'Sir Walter Scott was the first to publish this ballad, which came from an old woman who lived in Kirkhill, in West Lothian. The area is now part of Broxburn. There is no physical geography connected to Usher’s Well. Instead, it is a ballad location, such as Garland Town and Strawberry Castle, which cannot be mapped, and the ballad is perhaps all the better for it.
“The Wife of Usher’s Well” is, in effect, a ghost story, with three sons returning to their mother, but not being quite as they appear.'

That is from

http://walterscott.eu/education/files/2013/02/Interpretative-Notes-to-The-Wife-of-Ushers-Well.pdf