The County is an ancient geographical division of England. It is not an administrative division as such, though it began as one. There are 39 counties in England. Most of these have existed since Saxon times, with the northernmost ones generally established in the Norman period, and they continue to exist. See The Shiring of England for full information about how they came into being.

New levels of government were introduced in 1889, 1965, 1974, and in dribs and drabs from the mid 1990s. These are administrative, not geographic, divisions, and do not affect the existence or (in theory) boundaries of the 39 counties. But in practice the word 'county' is used to mean these too: the distinction I am making is not widely appreciated. People talk about the old counties having been abolished, when strictly speaking all that happened was that they lost their governmental function.

These are the counties of England, to the extent we can speak of permanent places:

Some notes on names.
  1. Devon, Dorset, Rutland, and Somerset are also less commonly known as Devonshire, Dorsetshire, Rutlandshire, and Somersetshire.
  2. Hampshire has also been known as Southamptonshire, though this name is obsolete.
  3. Four of them include regions wiith special status, and were sometimes known in full by paired names: These are traditional (pre-1889) and obsolete names, though the first was also used for an administrative area in later reforms.
  4. There is also Monmouthshire, one of the Welsh counties, which for certain judicial purposes was governed as part of England, so sometimes Wales was known formally as Wales and Monmouthshire.
  5. Many of the counties have an abbreviation; usually this is an obvious one ending in 's.' (Beds., Bucks., Cambs.), but some are less obvious: These are abbreviations, not alternative names.
  6. Durham has the unusual full form County Durham. (In origin because the bishop had princely powers within the county but also held "Durham" territories outside the county.)
  7. Officially (e.g. as Parliamentary constituencies) the names ending in "shire" were called after the town they took their name from, e.g. County of Worcester, County of Lancaster (for Lancashire), County of Chester (for Cheshire), County of Southampton. But Berkshire and Wiltshire were used because they're not named after towns. (I don't know about Shropshire.)

Shire and county are synonyms when describing a region. Shire is the Anglo-Saxon term, and county is a Norman term for an earldom. Earls were assigned to shires at roughly one per shire, but I don't think there was a formal requisite for this. But I haven't researched the mediaeval status, so can't commit myself.

Though the counties might have had some traditional administrative function (each county had a sheriff and a lord-lieutenant, for example), they were not the focus of local government. Most counties had hundreds, wapentakes, or parishes. Sussex had rapes, Yorkshire had its three ridings, Lincolnshire its three parts (the singular is 'parts'), there was the odd autonomous region like the Soke of Peterborough in Northamptonshire, and so on. A mediaeval patchwork quilt, and far too complicated for me to work out and present.

For parliamentary purposes, however, there was a difference between shire and county. In the traditional arrangement, formulated in the Middle Ages and not overhauled until the Reform Act of 1832, a county sent two members to parliament. Certain towns in the county might also have the right to send two members. These privileged towns were called boroughs, and its members were called burgesses. The rest of the county was called the shire, and its members were called the knights of the shires. The Cinque Ports and the Universities also sent members.

THE 1889 REFORM

In 1889 a new level of government was created, the County Council. Roughly, there was one county council per county, but many cities and towns were administratively independent of the county that contained them. These autonomous towns were called county boroughs.

Some counties were covered by more than one county council. In most cases this was by dividing larger counties into their traditional parts, but a new council was created for London metropolitan area to cover some parts of three counties. Where the administrative district did not coincide with a county, it was sometimes called an administrative county.

COUNTY                  ADMINISTRATIVE COUNTIES
Cambridgeshire          Cambridgeshire
   "                    Isle of Ely
Lincolnshire            Holland
   "                    Kesteven
   "                    Lindsey
Northamptonshire        Northamptonshire
   "                    Soke of Peterborough
Suffolk                 East Suffolk
   "                    West Suffolk
Sussex                  East Sussex
   "                    West Sussex
Yorkshire               East Riding
   "                    North Riding
   "                    West Riding
Middlesex }
Kent      } (some)      London
Surrey    }

There were also no doubt numerous minor adjustments, resolutions of mediaeval anomalies, simplifications of borders, and so on, as convenient.

THE 1965 REFORM

In 1965 a small change in County Council arrangements took place.
  1. Cambridgeshire and Isle of Ely councils were merged to form a single council called Cambridgeshire and Isle of Ely.
  2. Huntingdonshire and Soke of Peterborough councils were merged to form a single council called Huntingdonshire and Peterborough.
  3. London and Middlesex councils merged as Greater London, which also covered more districts of Kent, Surrey, and Essex.

THE 1974 REFORM

In 1974 a much more wide-ranging administrative reform took place. Now, the whole of England was covered by administrative counties, each of them roughly the size of a county, and in many cases coinciding with the counties they were named after. However, there were quite large boundary adjustments, as well as a few divisions and mergers.

I must stress once again, they are not Counties. The 39 counties have never changed. They're still here. Rutland wasn't abolished in 1974. Yorkshire wasn't divided into parts in 1974, nor in 1889. Yorkshire is a place. The following are governments, not places. I mention only the major differences between county and administrative county boundaries.

ADMINISTRATIVE COUNTY

These changes imposed on the 1889/1965 system gave the following administrative counties: Avon, Bedfordshire, Berkshire, Buckinghamshire, Cambridgeshire, Cheshire, Cleveland, Cornwall, Cumbria, Derbyshire, Devon, Dorset, County Durham, East Sussex, Essex, Gloucestershire, Greater London, Greater Manchester, Hampshire, Hereford and Worcester, Hertfordshire, Humberside, Isle of Wight, Kent, Lancashire, Leicestershire, Lincolnshire, Merseyside, Norfolk, North Yorkshire, Northamptonshire, Northumberland, Nottinghamshire, Oxfordshire, Salop, Somerset, South Yorkshire, Staffordshire, Suffolk, Surrey, Tyne and Wear, Warwickshire, West Midlands, West Sussex, West Yorkshire, Wiltshire.

THE 1990s REFORM

The uniform structure of administrative counties was discarded about twenty years after it was introduced, and over a number of years various levels of authority were brought in to replace them. This is the situation as described in Gorgonzola's write-up above.

One final word: Ugh! -- As far as I can tell, almost everything I've written above is roughly correct, but obviously in the face of such a system, there are bound to be little question marks everywhere. /msg me with corrections. (Evidence would be nice too.)