If you haven't already: Interview your still living family members to find out what they know. Parents, grandparents, uncles, aunts, cousins, the oldest people in your known family unit.
I interviewed a couple of my husband's elderly cousins, who gave me the name of their grandmother (very common Irish name), who is my husbands great great grandmother. Then as I cleaned my father in laws closets after he died. I found a funeral card for her and was able to get her date of death and a death certificate that listed her parents.
