A county is an area of a kingdom that is defined for the purpose of administration. In period, they only really existed in Britain, where the Normans had substituted them for shires, without changing the actual names of the shires. Much of the Welsh counties were established by Edward I in 1282. The remainder were formalized in the Act of Union in 1535.
A county may be divided up within into ridings, hundreds, sokes, wapentakes, wards, lathes and rapes. These could then be divided into tithings and parishes.
Some modern writers also refer to the dominions of European counts as being counties and those of earls being an earldom. Further research is required to determine whether this is also a period practice.
In Europe there were also areas ruled by counts, which were called counties, which occasionally managed to achieve independence from their original kingdom, and which may, for periods, have had sovereign status. An example lies in the Netherlands, where counts sought to remain independent from France and the Holy Roman Empire.
Counties in the SCA
In the SCA, there are shires but the corpora does not define any branch as being able to call itself a county, except as alternative name for a defined type of branch. This alternative must be approved by the College of Arms.