When every lead brings you back to the same brick wall, it is time to switch tacks and research your ancestor’s siblings. Since they are descended from at least one of the same parents as your ancestor, a search of their records may provide the missing pieces to your puzzle. Perhaps your ancestor was born before birth records were mandatory, but had a younger sibling whose birth was recorded. Early marriage records were often skimpy on details, but later marriages of siblings may contain further information such as birthplaces and parents’ names. Elderly or widowed parents may be found listed in the census with a sibling’s family. The informant who provided the information for your ancestor’s death certificate may not have known their mother’s maiden name, but a sibling’s certificate may yield further clues. Wills, probate and land records are also excellent sources to search for information on your direct ancestor through their siblings. If you don’t know the names of your ancestor’s siblings, you can often find them in census records, wills, probate records and obituaries. Even if your ancestor had no siblings, you can still trace them through other collateral lines, such as aunts, uncles and in-laws.

Family members have always told me that Mammy Pattie had a younger brother, Claude. He would have been born between 1898 and 1901 according to the dates of his sister’s birth and his mother’s death. I have yet to find a trace of him, however. Mammy Pattie also had 9 half-siblings (my great, great-grandfather seemed to really enjoy being married, as he did it three times). I was unable to learn anything new about Henrietta from the records of those half-siblings (she just didn’t live long enough for sibling records to be of much help), but they did help me flesh out the story of the rest of the family. Records of the siblings from the third marriage helped me to discover the first marriage and more siblings, for example. They also helped me to trace the life of Mack Crisp going both forward and backward from the time he was married to Henrietta.

For more information:

Kissin' Cousins - Determining Family Relationships
A quick tip on how to determine cousinship (first, second...), degrees of removal (once removed, twice removed...) and even double cousins.

Lessons Learned from Collateral Lines
By studying only your direct ancestral line, you are missing the opportunity to fill in holes and and depth to your genealogical research. From the Golden Gate Genealogy Forum.

Siblings and Cousins and Uncles, Oh My!
Juliana Smith discusses the pros (and cons) or researching collateral relatives.