Short Answer: Tolkien invented orcs.
Long Answer: Tolkien invented orcs as we know them, but certainly not the name itself. There were the Orks (I think that's what they're called) of greek myth, which were big 'ol sea monsters, as well as the Orkneys/(Insert Alternate Spelling here) who were an irish/early scottish tribe, and/or a group of islands north of modern scotland. Also, there's some mention of 'orks' or the like in Beowulf, which (as far as I could tell from my limited research) was in some capacity, a reference to the Orkneys, as well as the Orcaes (or something like that) who were deamons of Anglo-Saxon myth.
Now, of course, this is just what I've found after my own perusal of various sources, including Tolkien's foreward (or was it an appendix?) specifically about Orcs in LOTR, where he mentioned the greek sea-beasts, and how they were unrelated, as well as the Anglo-Saxon demons, which he attests to as the primary source for the term orc.
So, satisfied? Anybody else have more complete information?