Prepared by Elisabeth Lindsay.
In genealogy, a collateral ancestor is someone related but not in your direct line of descent such as an aunt, uncle, or cousin. A collateral line, then, is the family or lineage of a collateral ancestor. Collateral lines are the branches on the family tree. And going back in time, somewhere along the ancestral line, diverse collateral families merge to share a common ancestor.
When conducting research, collateral-line families can be extremely important and may even help you break through that long-standing brick wall. One of the primary steps in the research process is to see what others have done, This step aims at helping you avoid duplicate research by connecting with someone else in your family who might be working on your same line with whom you can share information—perhaps a distant cousin, a member of your collateral line. Collateral-line families are also important to your direct-line research. In the absence of information on an elusive ancestor, one of the best ways to gain more information is to conduct vigorous research on the siblings within a family. These are collateral-line ancestors. You may be surprised at how much you can learn by researching the other members of your ancestor's family. For example, tracking the births and marriages within a family may help determine a family's migration and places to look for documents. Even by talking to your own aunts, uncles, and cousins, one person may hold the key to many unanswered questions.