I hope you're not getting too confused, BeauD - these are two completely different songs with different tunes. Both lovely, but in no respect interchangeable.

The one you're asking about is the Copper family version. As Snuffy says, the chords aren't written down in their version, they're supplied by the voices, but it's really just a three-chord trick (D, G, A), with the odd relative minor if you want to be clever.The Coppers sing it in D. I shoud think C or D would suit most voices, you'll have to try it out with your mandolin.

Low Lands of Holland - Dolores Keane's tune (on the recording I have)is the major-key one that sounds a bit like a Scottish pipe tune, as opposed to the modal/minor one that sounds a bit like Star of the County Down. Great tune, but the melody has quite a big range and jumps for the singer. Again, there's nothing tricky about the chords, just the obvious ones will be fine. She sings it in A but that's really quite low for most voices. C or D might be better.

I think you should have tracked down the words by now with the links above, but let me know if you're still searching.