What is an Earl?
A earl is the oldest English title of nobility, ranked in the modern peerage between marquess and viscount. The dignity is equivalent to the continental European "count." The wife of an earl bears the title of countess.
The word "earl" is related etymologically to the Norse and Danish word jarl, meaning hereditary chieftain. Originally it meant simply a nobleman, one who possessed five hides (or about 600 acres) of land. From the reign of King Alfred (871-899) certain of these noblemen received responsibility for governing the various administrative districts, or shires, into which England was being divided. These royal officials were known as ealdormen until the reign of Canute (1016-1035), when the title of earl was created for them. In Anglo-Saxon England each ealdorman served with the local bishop and sheriff as one of the presidents of the shire court.
The jurisdictions of the Anglo-Saxon ealdormen were not coterminous with the counties, and before the Norman Conquest there were always fewer ealdormen than there were shires. In fact, the number of earls had so diminished and their individual powers so increased by 1066 that they virtually controlled the central government. William the Conqueror recognized the dangers of this system, and it was he who equated the earldoms with the counties. From his time the office became more and more an honor, rather than an administrative position. In 1328 the first earldom (that of March) that did not carry a county jurisdiction was created.
In modern Britain the heir of a duke or marquess receives the courtesy title of earl.