I wrote the following about the size of magical population. Since the message will get buried under the thousands of other comments, I'll just copy-paste it here so that at least you rational people can read it.

"The size of population of wizarding Britain and all of its implications.

In the books it is never mentioned how many magical people live in Britain. However, we can do a bit of calculation.

In the Deathly Hallows (Chapter 11) Lupin mentions that nearly every British witch and wizard is educated in Hogwarts. In the Prisoner of Azkaban (Chapter 15) it is mentioned that there are two hundred Slytherins cheering for the Slytherin Quidditch team. If every Slytherin was present, that means the size of a Hogwarts House is 207 (spectators plus players). If every House has as many students, the total number of students in Hogwarts is 828. As education in Hogwarts lasts for seven years, and a small minority does not attend Hogwarts, that means a British age group of magicals is about 120. Magical people appear to live very long. I'm not sure if Dumbledore's age has been confirmed in the books, but he was a bearded man in 1938 when he first met Tom Riddle. In the 1990s Griselda Marchbanks, who oversaw Dumbledore's OWLs, is still active, as is Bathilda Bagshot, whose great-nephew is the same age as Dumbledore. Maybe we could estimate that on average magical people live to the age of 120. 120 times 120 is 14,400. However, most magical families appear to only have one child, and childlessness is very common (Albus and Aberforth Dumbledore, Voldemort (in the books, anyway), Snape, Sirius, Pettigrew, Crouch Junior etc.). That means the older age groups are probably larger. (Of course, there is some inflow of Muggle-borns and foreign magicals.) So, the total population is about 15,000.

However, wizarding Britain appears to be just a magical version of Muggle Britain, everything implies that. The Ministry of Magic has a vast bureaucracy that appears to employ a large portion of the population. What are they all doing?

The total population of the British Isles is about 67 million. Diagon Alley and Hogsmeade are the only non-Muggle settlements, so apparently magical people live among the Muggles. If they are distributed across the Isles in the same proportion, that means there are about 12,000 English magicals, a little more than 1,000 Scottish and Irish magicals, and less than 1,000 Welsh magicals. Then why are there separate English, Scottish, Irish, and Welsh national identities among wizards? Why don't they all mix up into one nationality? It would make sense, because they attend the same school, and magicals don't have social or logistical limitations based on geography. We know that each one of the nationalities has their own national Quidditch team. The Irish team is superb, but who are the players, actually? They attended Hogwarts, right? Did they totally rule the Hogwarts Quidditch championship? When did that happen? Why are they so much better than the Gryffindor Quidditch team? Does one have to graduate before he/she can become such a Quidditch virtuoso?

Then there is the question of The Quibbler. It is a magazine for weirdos. Perhaps one percent of British magicals read it, and that's 150. And since most of British magicals appear to live in families, and family members read the same copy, The Quibbler's distribution is perhaps 50. It is published monthly. How does a family provide for their living by selling 50 copies of a magazine a month?

The Ministry of Magic made the Daily Prophet its medium of propaganda. That works if the population is huge. However, it is impossible to prevent ideas from spearing to the whole population, if the population is about 15,000. Just by telling rumours to friends and relatives and asking them to do the same one can quickly make sure that everyone will hear them."