"人口" 的英文是 "population", 所以 "这个城市里有多少人口" 可以说成 "What is the population of this city?"。
关于 "population" 的来源，它来自拉丁语 "populus"，意思是 "人民"。
一些关于 "population" 的例句:
The population of New York City is over 8 milpon people. (纽约市的人口超过800万人。)
The population of the world is expected to reach 9 bilpon by 2050. (预计到 2050年世界人口将达到90亿。)
The population of this small town is only 500 people. (这个小镇的人口只有500人。)