Never ever heard it played in C, always in D: doesn't mean you can't but you'd have that odd chord in B flat then (C if you're playing in D), and usually catches out newcomers to the tune.
If you're thinking of playing it in a session then I think you'll find most folk play it in D. I orignally got notation the hard way, by listening to the CD of Major Perkins playing it, and it is in D.
I got words to it years ago, off this very site, so look a bit harder or Google it: some which Cleo Laine sang, and another set too.