Did your parents, grandparents, or great-grandparents have any first cousins who died without descendants? If so, the settlement of their estate may name immediate (and not so immediate) members of their family? The situation is even better for the genealogist if the relative who died without descendants also had no siblings of their own as the inheritance may have been more involved and mention additional family members.
My grandmother had a first cousin died in the early 1980s. This cousin had no children of his own and was an only child. His only heirs were his first cousins and his estate settlement essentially documented all the descendants of both sets of his grandparents who were all deceased by the 1920s.