Why do we say County Durham?
In Ireland all the counties are expressed as 'County....' followed by the name, e.g. County Kerry, County Galway, County Clare etc. This equally applies to the six counties north of the border, County Down, County Londonderry, County Antrim etc.
This style is not used anywhere else in the United Kingdom, where the counties of England, Scotland and Wales are simply known by their names, without the word 'county' appearing before, or in the American tradition after the name. We simply say Lancashire, Surrey, Norfolk etc.
There is one unique exception to this. That is County Durham. We always speak of County Durham, as if it were Irish. Does anyone know why?
Solution 1:
Having searched and found no definitive answer, here is my best guess.
In the Middle Ages Durham was important politically as it was a buffer state between England and Scotland. From 1075 (after the Norman Invasion) the Bishop of Durham became known as a Prince-Bishop, granted certain autonomous powers such as the right to raise an army, mint his own coins, and levy taxes, on condition he remained loyal to the English (ie Norman-French) king and fulfilled his role of protecting England’s northern frontier.
County comes from the Old French term, conté or cunté and could denote a jurisdiction in mainland Europe, under the sovereignty of a count or a viscount. - ie, it was a word used by the Norman conquerors in England.
Shire on the other hand is an Old English word already given to many parts of England before the Norman Conquest.
Similarly, Ireland was never invaded by the Saxons but was conquered by the Normans. Thus the areas under direct French Norman rule - Ireland and Durham - were known as counties, while the shires of England retained their English shires.
You can find a parallel to this with food words - cows and sheep were the animals tended by the Anglo-Saxon peasants, beef and mutton were the meats eaten by the French nobility.
And the reason county goes before the name instead of after it is because the French speak backwards :)
Solution 2:
According to Wikipedia, the surprising answer seems to be
The former postal county was known as "County Durham" to distinguish it from the post town of Durham.
It seems that usage has become common.