My ancestors were Duhig's from County Kerry. It is pronounced Dewey. They (Great-great- grandmother Margaret Gaynor Duhig, great grandfather Maurice Duhig and his two brothers John and Michael) came into New York in 1853 and settled in Elroy WI. Everyone's names, except John, were changed to Duffy.
When my husband and I were in Ireland in 1997 we stayed in a B & B in Blennerhassett just outside Tralee and asked about Duffy's in the area. We were told that there never had been any. I told the woman that it was spelled Duhig (I pronounced it as doo-hig) and she said: "oh, Dewey" and then said the last Duhig in the county had moved to Cork to become the Governor of the Prison.
I understand the name to mean "black" just like Duffy and that it is probably a Gaelic shortening of the Gaelic spelling of Duffy.
Found no graves and all the church records prior to 1867 were missing. Disappointing.