I got this ask last week, but since the answer is lengthy and it’s reference material I will probably want to find again, I’m publishing it as a post.
Anonymous asked: About half a million titans? Where did the First King found such amount of people? How many people are living inside the walls anyway? Or rather lived, I remember a lot of people died after Collosal titan’s invasion.
What is the current population of the walled world?
We have a good idea of how many people are living within the walls after the fall of Shiganshina. Episode two on the anime states that 250,000 people died in the sham effort to reclaim Wall Maria. The manga calls that same number 20% of the population.
If we take both numbers as canon and do the math, it means there were 1.25 million people before the operation to reclaim Wall Maria and 1 million after. So the current population inside the walls is around 1 million people.
The 250,000 that were sent out were refugees–survivors of the fall of Wall Maria, so it represents only a fraction of the original population. I’d guess the original population of Wall Maria, including the outlier districts was close to a million before the wall fell. (Edit: @daylelight makes a good argument that this number might be much lower.)
How many titans are inside the walls?
According to chapter 86 the manga, the number is “tens of millions”, but it’s likely that number was Marleyan propaganda intending to scare the population.
I’ve seen several posts on Reddit where people have calculated the circumference of the walls and the size of the titans. They put the number closer to half a million or less. I believe numbers are closer to the truth.
Who are the people contained within the walls?
I don’t know if we can trust all the history contained in Chapter 86, but it claims that the walls were in place before King Fritz brought his people there. This matches much of the art and mythology we’ve seen. The walls were in existence before the people came.
With all that in mind, it makes sense to me that the mindless titans contained inside the walls are the original residents of Paradis Island. And my personal fun head canon is that this is why the East Sea Clan is basically extinct :)