Many people with Gaelic origin surnames are interested in researching their clan connections. This is cannot be done by simply assuming one’s last name is also a clan surname. Many Gaelic surnames are not clan surnames and do not relate to historical clans. They are surnames created from Gaelic patronymic naming customs. Many Gaelic surnames did not develop a fixed form until very late, circa 1500s into the 1600s. Even then the use of clan surnames was not universal and was often a form only found on legal documents written by government officials, rather than the surname a family actually used in their community. Clan surnames were used more by older sons of landed families. In some cases families related to a historical clan via marriage, via legal contracts such a manrents (military obligations to a lord), tacsmen (land managers) or just allies, would take the surname of the clan to which they were associated. The best way to research one’s clan connections is through Y chromosome DNA testing (Y-DNA) and a study of the history of a district that the family originated.
Y Chromosome DNA (Y-DNA) testing usually provides a kinship group of families that share the same paternal kinship. Often the non-surname matches are as important as the surname matches when confirming clan connections. In the primary sources often a group of surnames are associated with one clan or sept that will fit this kinship group of families.
If you have tested your Y-DNA at the 67 or 111 and a definite kinship group has appeared the surnames in the group usually give data relevant to past clan connections. A good first step is to have research done on the etymology and history of those particular surnames. Sometimes this alone reveals a family past clan connections. For example, the common Ulster and west Highland surname of Campbell. This surname is usually anglicised form of Caimbeul from the well-known Argyll family. But some Campbell families have a kinship group that includes the surname Caulfield, which is an anglicised form of the name Mac Cathmhaoil, a county Tyrone Irish Gaelic family. This family used both Caulfield and Campbell as anglicised forms of their surname. Another example is the surname McDonald/McDonnell, that is from the Gaelic name Mac Dónaill. The surname books will inevitably link the anglicised form to the great Clann Dhónaill; in fact, many clans had branches named Mac Dónaill, in both Ireland and Scotland.
If one of your research goals is to explore your clan connections and you have reached a brick wall with your paternal kinship group matches it might be of help to have an expert look at the group and to an analysis of them. This involves an etymology study of the surnames in the group and a history of the surnames along with geographic connections to the group and an examination of any primary sources. It is complex work often working with Gaelic language sources, but can provide insight into a family’s clan connections.