The Historic counties of the United Kingdom are ancient geographical divisions of the United Kingdom. Although not defined by any one function, over many centuries, various forms of administrative function have been based on them. These have included the areas of Parliamentary constituencies, the Court of quarter sessions, the areas in which a Lord-lieutenant and Sheriff serve, territorial units of the Militia, as well as the basis of the original county councils. Although these areas have subsequently changed, the historic counties on which they were originally based have not. The Office for National Statistics recommended them in the Index of Place Names as a stable, unchanging geography which covers the whole of Great Britain.
