The United Kingdom, also called the United Kingdom of Great Britain and Northern Ireland and often referred to simply as "Britain" is a constitutional monarchy and unitary state. It is headed by the British Royal Family, which rules underneath a common, constitutionally created legislature. Within the United Kingdom are four home nations of distinct cultures and histories: England, Scotland, Northern Ireland and Wales.

The interior of the United Kingdom has divided itself into legislated and symbolic counties for hundreds of years, based upon electoral power, religious significance, clans, landowners and landscapes. The borders and scope of these counties has consistently changed, with most being redefined several times. For most of the home nations, with the exclusion of Northern Ireland, county lines were again redrawn at the end of the 20th century, and those definitions have been utilized here.

In 1996, England was divided into 47 Ceremonial or Geographic counties. Each is assigned a Lord-Lieutenant, a representative of the monarch, and is defined by its metropolitan and non-metropolitan areas combined with its geography. The term Lieutenancy is also sometimes used for these areas.

Northern Ireland consists of six well-recognized counties. Armagh, Fermanagh, Londonderry and Tyrone were all created in 1584, and the origins of Antrim and Down likely go back even further, perhaps into the 13th century. Occupying the top part of the island of Ireland, Northern Ireland was created in 1921 under the terms of the Government of Ireland Act of 1920. Its six counties previously made up part of the province of Ulster, and had a Unionist majority. Ulster was divided, with its remaining three counties being merged into the Republic of Ireland.

Underneath the Local Government Act of 1992, Scotland's Regional Councils were abolished and 32 Unitary Councils were created. Some of these Unitary Councils are comprised completely of Scotland's larger cities and their surburbs, such as Greater Dundee, Greater Edinburgh and Greater Glasgow. The city of Aberdeen is considered a Unitary Authority on its own, but has been included here in the county of Aberdeenshire for simplicity's sake..

The counties of Wales are referred to as the Preserved Counties, and were created in 1994 by using the basis of the Administrative Counties, created by the Welsh Local Government Act of 1972. The Preserved Counties are used for the purposes of Lieutenancy, and are only slightly different from the original Administrative counties, with minor changes having been made to encompass the whole of historical boroughs and to better reflect local government boundaries.

Below is a complete list of abbreviations, counties, their main county town/city and their country in the United Kingdom.