I have been researching my Gallagher ancestors from islandeadsy parish since 1979. With the help of Gerry Delaney at the Mayo South Research Centre in Ballinrobe, I have learned that the Gallaghers were from Raheen Barr. There are church records that indicate Daniel Gallagher and his wife Nancy Gillespie had three children there. My great great grandfarther, Martin Gallagher, is listed in the baptismal records as being a baptism sponsor for one of Daniel and Nancy's children.
Martin and his brother, Patrick, left Mayo for America in 1847. The next record I've found is their appearance in the 1850 U.S. Census of Hoosick Falls, New York. Martin was living with Francis Carpenter family. Patrick was living with John Gallagher, whom I assume was a relative (brother?). In 1853 Daniel and Nancy have a son, Daniel, Jr., in Hoosick Falls.
Later (1850s) Patrick, Martin, Daniel, and another brother, Hugh, moved to Waukesha, Wisconsin. Patrick and Martin then moved to Fond du Lac County, Wisconsin.
