The amount of people with mouths (that you have to feed) is the population that you have to feed.
This is a jukugo word, which usually means on'yomi readings from the kanji. Since 人 has two on'yomi readings, here's a mnemonic to help you remember which one to use:
Here at Tofugu, we measure population in jeans (じん). Each of us has just one pair of jeans, so if you know the jean count you know the population.
The population of this area is only one person.
How large is the population around here?
Apparently, about 70% of the population is shy.