Yea, Greg: Lonnie Donegal recorded it in 1959, on a Pye single, the very first I even bought, age 14, little did I know where it would lead, still got it! The flipside? "Kevin Barry".

Yes it's definitely the Lagan near Belfast. Campbell was born in Castlereagh Road, east Belfast, just a couple of miles from the Lagan. In his youth he suffered from some "nervous" problems and often went for long rambles along the Lagan's banks, joining the River at Shaw's Bridge. There are quite a few other references to the geography of this area in some of his other poems.
The Donegal "Laggan" theory is though an interesting diversion. I always regard "My Lagan Love" and the "Gartan Mothers' Lullaby" as virtually "sister songs" (the language used in both contains many identical words and phrases), what I can't understand is why he separated them geographically by a hundred miles, which in Ulster in 1904 was a long way?

"the crickets singing stone" is a reference to the folk custom of, to quote Campbell in the "Songs of Uladh", "in South Ard Macha [Armagh]when a young married couple are about to take up house for themselves, it is a custom with them to carry a brace of crickets each in a match-box from the old parents hearths, these to bring luck to their own, and when secured to hold it there."                     

He says that the lenanshee, "leanan-sidhe" was "a fairy mistress who seeks the love of mortals...she is the Gaelic muse...the Gaelic poets die young, for she is restless and will not let them remain long on earth, this malignant phantom".                                 

Campbell spoke Irish well: his grandparents were native speakers on a farm at Flurrybridge, South Armagh, and he used to spend his summer holidays there.

Campbell is said to have been a cousin of Ethna Carbery, can anyone elaborate on this?