What you also need to remember is that often an Earl will have a more senior title e.g. The Earl of St Andrews is better known as The Duke of Kent (and his son uses the Earl of St Andrews title as a courtesy title to indicate that he is the heir).
Not all Earls as directly associates with counties either but often cities or in the case of Prince Edward a place that no longer exists.
Just the royals who are earls as well as dukes:
Earl of Merioneth (Philip)
Earl of Chester (Charles)
Earl of Strathearn (William)
Earl of Inverness (Andrew)
Earl of Ulster (Richard - The Duke of Gloucester - his son uses the title)
Earl of St Andrews (Edward - The Duke of Kent - his son uses the title)
Then there is Edward:
Earl of Wessex (Edward)
Earl of Snowdon - ex-husband of Princess Margaret is another connected to the royals with an Earldom.
Earl of Harewood is also related to the royals being descended from George V through his daughter, Princess Mary.
The Wikipedia list does say whether there is a current holder of the title - and is comprehensive in that regard.
The terms it is using have meaning:
ALL the titles with the word 'extant' in the second last column tells you whether there is a current living title holder, and the final columns tells you whether or not that title is the subsidiary title of a duke or marquis.
There are currently 323 (according to my count on Wiki and I may have missed one or two or counted one of two twice but...) extant, or existing, earldoms in Britain - some English, some Scottish and some British, some peers holding multiple earldoms along with other titles while others have the earldom and maybe one other.