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My inner historian is going insane over the North somehow having less than a million people. 

I calculated it out - I saw a ballpark for the North having around 1.2 million square miles, which comes out to about .8 persons per square mile if we assume the North actually has an even one million. By contrast, Scotland in the mid 1300s is estimated to have had half a million to a million people. Scotland is about 30k square miles - meaning, if we go with the 1 million estimate, Scotland would have had a population density of around 33 people per square mile. 

Even if we half the area of the north and say half of it is uninhabitable or whatever - that still leaves us with an area the size of Iran. 

Even accounting for the long winters, this is kind of ridiculous. 
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