Tim seems to have the dates wrong - rather than the authorship. The poem is definitely by J K Casey a.k.a. Leo. I recently picked up a copy of "Reliques of John Keegan Casey" published in 1878. It's in there as part of the "Amatory Poems" mentioned by Tim.
Coincidentally, I've been promising to show Tim the book - but keep either misssing him, or leaving it behind me on my way to festivals!