I am looking for some sources that give me an idea of how many humanoids of the different races live in the inner sea. Best would be if I can get information for each country. I have the Inner Sea Guide but could not find anything in it.
There are sources, because paizo developers decided to not list those population values when they created the Inner Sea World Guide. There will be population specifics for towns and cities, but not for regions or countries.
While the lack of a population total for each nation was a specific choice by us, I can see how that might be off-putting to some readers. This might be something that we'll revisit if and when we reprint the Campaign Setting, and that might be a better time anyway for us to make those decisions since now we're two years-worth more familiar with the setting than we were when we first created it, of course... and are more confident about what nations we DO want to be populous and what ones we don't.
Alternatively, you could just look at the population figures for the major cities that we list, total them, and then just increase that total by, say, an extra 50% or so to get a ballpark figure. (WARNING! I just pulled that percentage out of the blue, so it might not end up being accurate in all cases!) Most of the citizens of a nation are going to be denizens of the big cities anyway, since we want to leave large parts of each nation wilderness for adventure purposes.
Meanwhile, the Pathfinder Wiki has information that has been published on the several adventure paths and campaign settings regarding specific towns (examples: Wati, Absalon, Sandpoint, etc). Just check if the town you are looking for isn't already listed there.