English Translation
The population remains stationary.
What’s with the でいる?
The Japanese sentence sounds very unnatural…
いる literally means “being” and じっとしている, for example, means “don’t move and is still” or “being in the same position.” We often use いる when the subject is an animated creature, but we don’t use it for 人口 (the number of residents in a certain area.)
My alternative translations are:
人口は変わらぬままだ。
人口の増減はない。 (pron. ぞうげん)