While I might quibble on some of the finer points, the essay at the bottom by an amateur is a pretty good summation.
Since coats or arms are mentined in it below, I would point out, though, that unless you can prove direct lineage to the person actually awarded a coat of arms, you are technically not permitted to display or claim them as your own. The coincidnece of a family name is not enough to claim an existing coat of arms. See The Office of the Chief Her ald at http://www.nli.ie/
The arms mentioned below are actually Scots, I believe, not Irish, though I have heard of another set of arms that includes some of the same elements that are apparently associated with another Strain, minus the thistle (the Scottish national symbol, as the shamrock is for Ireland), the crest is an arm holding a sword, etc.
There are a number of other variants on the name not included below (Strayhorn, Strathairn, etc.), however. Hope you enjoy it:
ORIGIN OF THE STRAIN FAMILY SURNAME
Whether the Strain ancestors prior to the 12th century came from Ireland or Scotland is simply impossible to know. However, we do know that they are unlikely to have originated from anywhere else as all the evidence available today points to the northern British Isles. At any rate, to try and differentiate between Scotland and Ireland in that period would be futile. At their closest point, the two countries are separated by only 21 miles of the Irish Sea, and in times of hardship people moved back and forth between the two regularly and nationalities were blurred.
You should also keep in mind the the Dalriadic Scots, who ended up giving Scotland its name migrated from Ireland in the 5th century AD or thereabouts. Most if not all the Gaels who eventually settled in the Isles were probably from Ireland, moving into empty territory and eventually conquering and assimilating the Picts. It is unlikely that the Strain name originated with the Picts, of whom we know very little. However, with the assimilation of the Picts by the Gaels there is a good chance that there is some Pict blood in our veins still!
Most of the Eurpoean surnames in countries such as Ireland and Scotland were formed in the thirteenth and fourteenth centuries. The process had started somewhat earlier and had continued in some places into the 19th century, but the norm is that in the tenth and eleventh centuries people did not have surnames, whereas by the 15th century most of the population had acquired a second name. The first people in Scotland and Ireland to acquire fixed surnames were the nobles and great landowners, who called themselves, or were called by others, after the lands they possessed. Surnames originating in this way are known as territorial. Formerly, lords of baronies and regalties and farmers were inclined to magnify their importance and to sign letters and documents with the names of their baronies and farms instead of their Christian names and surnames.
The Strains are undoubtedly of Celtic origin. There are two possible lines of origination; one in Ireland and one in Scotland. The Scottish version of the surname was a locational name, local from "Strachan," a town in Kincardineshire, Scotland. Early record of the name mention Walderus de Stratheihan with consent of Renulfus, his son and heir, granted the lands of Blarkerocch to the church of St. Andrew in 1200 AD.
The Irish version began in Ulster and the main evidence comes from an entry in the Annals of the Four Masters, a medievel manuscript written by Irish monks recording the history of Ireland. For the years 1204 AD they have an entry referring to Sitric O'Sruithen (meaning "stream" - this is why some members of the Strain ancestors took the name Bywater) which read, "Sitric O'Sruithen, Erenagh of Conwal, i.e. head of the Hy-Murtele, and chief man of all the Clann-Snedhgile for his worth, died, after exemplary penance, and was interred in the church which he had himself founded." This is the Irish name that the names Strain and Strahan are believed to be derived from. The associated arms are recorded in Sir Bernard Burkes General Armory, Ulster King of Arms in 1884.
ARMS - Or a hart at gaze azure attired sable.
CREST - A demi stag springing or holding in his mouth a thistle proper.
MOTTO - Non timeo sed caveo (I do not fear but am cautious).
The Strains in Ireland are predominant in counties Donegal and Down. My own belief is that the Down Strains are more likely to originate from the placename Strachan and the Donegal Strains probably originated from Sitric O'Sruithen. I don't have much evidence for this except that Down is close to Scotland in the east, and Donegal in the west is where Sitric is buried. However, it's important to remember that although Strain is not a common name, it is quite common in Ulster and much less so in Scotland, with the majority of Scottish descendents still using the name Strachan. The Scottish Strains or Strachans most likely migrated to Ireland during the Plantation of Ulster in the early 17th century. Due to religious issues, and constant attacks from the locals, most eventually moved on to America and became known as the Scotch Irish or Ulster Scots. But that's a whole other story!
By Damian Strain (c)2001.