I have a Michael Gilligan who was b abt 1823. his parents were Michael Gilligan and Winefred Kivlehan. There is a good possiblity that he came from Sligo. He came to the US sometime in the 1840's. He settled in Dubuque Co. Iowa and married Mary Cullen. I believe he had at least 2 brothers who may have come with him. The story has come down through the family of someone in NY, but we don't know who or where for sure. There were other Gilligans in Iowa and I believe that a James could be a brother also. I know there was a Julia Gilligan who's picture I saw with small children and it was taken in Cedar Rapids, IA.
Let me know if any of this is familar and I'll go through my notes for more accurate information.