As a result of genealogical evidence we know that some Strachans from Scotland who emigrated to Northern Ireland (i.e., Ulster Plantation) changed their surname spelling to Strain between the 17th and 19th century. Conversely, we also know that some Strains are of Irish decent, and are not related to Strachan. The picture is not absolutely clear where the Strains came from - whether they descended from the clan of the Irish chieftain O’Sruitheain of Donegal, or if they came to Ireland from the Scotland. It is also possible that the Strain surname has several different origins and that not all Strains are related.
Given the aforementioned, the Clan Strachan Society therefore treats the STRAIN surname as a derivative spelling of the STRACHAN surname. HOWEVER, out of respect to those who insist they are descended from the Irish Chieftain O’Sruitheain of Donegal and wish to celebrate their Irish heritage, we also recognize and further acknowledge that not all Strains (broadly defined) are Strachans. STRONG surname and variations included are similar sounding surnames (e.g., Straughan), etymologically equivalent names (e.g., Strachan), surnames that may have been shortened to Strong (e.g., Strongman, Stronger), and surnames that might be mis-recorded or misperceived as Strong (e.g., Strang). According to one online source, the surname might also be a contraction of Armstrong, also a Scottish surname.
Thus, out of respect to those who insist they are not descendant from the Strachan line, we respect that part of your heritage, and acknowledge that not all Strongs (broadly defined) are Strachans.