I was looking at a comment here, and realized that I don't know what percentage of wizards are born to wizard families, and what are born to muggle families? Anyone out there know the answer?
In Chamber of Secrets, Ron says,
“Most wizards these days are half-blood anyway. If we hadn’t married Muggles we'd've died out.” (CoS – Chapter 7)
Sirius Black tells Harry in Order of the Phoenix that most “pure-blood” wizarding families have both Muggleborns (Ted Tonks) and half-bloods (Nymphadora Tonks) in their family tree, but don't want to acknowledge it. He also notes that there are so few "pureblood" families left that they are, by that point, all interrelated.
“The pure-blood families are all interrelated. If you’re only going to let your sons and daughters marry pure-bloods your choice is very limited; there are hardly any of us left.” (Sirius Black – OotP – Chapter 6)
On her website, J.K. Rowling says:
Don’t forget that, as Sirius revealed in Order of the Phoenix, none of these families is really ‘pure’ – in other words, they merely cross Muggles and Squibs off the family tree and pretend that they didn't exist. But yes, the number of families claiming to be pure is diminishing. By refusing to marry Muggles or Muggle-borns, they are finding it increasingly difficult to perpetuate themselves. This subject is touched upon in Half-Blood Prince.
The expressions ‘pure-blood’, ‘half-blood’ and ‘Muggle-born’ have been coined by people to whom these distinctions matter, and express their originators' prejudices. As far as somebody like Lucius Malfoy is concerned, for instance, a Muggle-born is as ‘bad’ as a Muggle. Therefore Harry would be considered only ‘half’ wizard, because of his mother’s grandparents.
If you think this is far-fetched, look at some of the real charts the Nazis used to show what constituted ‘Aryan’ or ‘Jewish’ blood. I saw one in the Holocaust Museum in Washington when I had already devised the ‘pure-blood’, ‘half-blood’ and ‘Muggle-born’ definitions, and was chilled to see that the Nazis used precisely the same warped logic as the Death Eaters. A single Jewish grandparent 'polluted’ the blood, according to their propaganda.
It appears that “pure-blood” families are becoming less prevalent; half-bloods comprise the majority of the Wizarding population; Muggleborns are less prevalent than half-bloods, but are perhaps a slightly higher population than pure-bloods. If I were to throw out some numbers, I might guess 15% pure-blood, 65% half-blood, and 20% Muggleborn. Something along those lines.
It’s interesting that Muggleborns are descended from Squibs, who are pure-blood wizards who lack the dominant magic gene (but who apparently still carry it as a recessive trait).
The corollary is that wizards born to two Muggles must be incredibly rare, because there are so many Muggles and so few wizards. Given 40 or so wizardly children of the same age in the UK out of around 644453 births per year and the only known fact that two Muggle-borns were in the same year as Harry gives us something like 1 per 320000 births.
This implies that around 375 Muggle-borns are born world-wide per year, if we assume the distribution of the Muggle-born wizards is uniform across the planet. If there were pure-bred families in other places then I think it's plausible that a population of wizards with 1 or fewer Muggles among their immediate 32 ancestors could be maintained forever if those individuals/families all wanted to do so.
I dont think the exact percentage was ever stated. But it's undertone that it is fairly low.
J. K. Rowling made draft list of students in Harry Potter's year :
[...] the year group is to compose of 40 students, 10 belonging to each house [...]
It gives 38/40 = 95%. But we don't know the lineage of all students, and there is at least 2 other student that are listed as Muggle-born in this list, but later works contradicted it.
So, we could safely guess that a fairly high percentage of wizards are born from wizard families, probably in the vicinity of 90%, plus or less 5%.
I would probably say around 20% Pure Bloods are still around, Draco Malfoy is a pure-blood and some other Wizards and witches , was it Salazar slytherin , Godric griffindor and the other two are pure bloods? And they have decendants such as Ginny who opened the chamber of secrets although she isn't pure blood... Probably most wizards are Half-Bloods such as , Ginny , Ron , Fred , George , Percy and so and so, there mother isn't actually a witch or it's their dad that isn't a wizard , either way their family was married into the wizarding world, I think around 50% Of wizards these days are Half Bloods. Now we come to Muggle born wizards , now I'm gonna use the other name for them and I appologise if I offend you with it... Mud-bloods. Hermione granger is a Mud-Blood and so is Colin but other than that they don't come into the story much , Also I forgot Luna is a halfblood