Originally, the land under the jurisdiction of a count (in Great Britain, an earl, though the original earldoms covered larger areas) by reason of that office, a county has since tended to represent a geographical unit of administration intermediate between the larger state or province, and the smaller township or municipality.
United Kingdom
English county -- in England, the county boundaries have varied considerably over the centuries.
The counties of Wales and Scotland were radically reorganised in the 1970s, giving way in the latter case to a reduced number of regions. These and the eight reorganised counties of Wales were in turn abolished in 1996 in favour of smaller unitary authorities, a system similar to that proposed for most of Great Britain in the 1960s.
USA
The term county is also used in 48 of the 50 states of the United States for the level of local government below the state itself. Louisiana uses the term parishes and Alaska uses boroughs. The power of the county government varies widely from state to state as does the relationship between counties and incorporated cities. In New England, counties function only as judicial court districts and most local power is in the form of towns.
France
The historical counties of France were abolished in 1790 and incorporated in the new départements created following the Revolution. The term survives, however, in the name of the Franche-Comté region, the former Free County of Burgundy.
China
County is the general English translation for the Chinese term xiàn (县 or 縣 pinyin xian4) which marks the level of government below the province. Such nomenclature was adopted since the establishment of the PRC. The number of counties in China proper numbers about 2000.
Prefecture was used for describing the same adminitrative region before PRC.
see Prefecture
Japan
In the Japanese system, prefecture are used to translate an adminstrative district about the size of a county.