I didn't think of that until after I'd already googled it, so I'll tell you my results anyway.
According to a site I found, the surname Joplin originated in Northumberland.
Do do do do do do do do. Do do do do do do do, do do do! (That's supposed to be the Maple Leaf Rag, which I started singing as soon as I read "Joplin.") :)
**Vita Brevis, Ars Longa**