Murphy is one of the most common names in Ireland. They are probably from every county. Check and see what other families they married into before immigration, and perhaps one of those families is located in a smaller section of Ireland. For example, if they married an O'Driscoll, they might be from West Cork, where that name is most prevalent. If they married a Sullivan, they might be from the O'Sullivan Beare peninsula in County Kerry. If they married Burke's there might be a connection to Galway Bay. If they married O'Keefe's their might be a connection to North Cork, etc. But remember families moved around since the 1640s when Cromwell sent the Catholics "to hell or Connaught", making them move to less desirable land in south west Ireland, similar to what the Americans did to the Indians in the area which became the United States. Read Irish Families, More Irish Families and Supplement to Irish Families by Edward McLysaght to gain insight into traditional areas originally inhabited by various families and clans.