The series overspent the budget, with each episode costing more than $1.78 million.
Dongnae, the city where the zombie plague first broke out, is an old name for Busan. Ironically, Busan was the safest place in Korea in another Korean zombie movie, Train to Busan (2016).
The series is adapted from the webcomic series The Kingdom of the Gods, authored by Kim Eun-hee and drawn by Yang Kyung-il.
The notice in Episode 1 that is ripped down has Traditional Chinese writing on it - which might confuse some viewers because this is a South Korean production. Korean as a written language, Hangul, was not invented until the 1440s; the educated and upper-classes read and wrote in Traditional Chinese. Even after Hangul was created (the intention was to help the less educated learn how to read and write), there was backlash from the upper-classes, and in the end, it wasn't widely adopted until the late 1700s/early 1800s.
It was originally planned as an eight-part series, but when the internal premiere received good responses, it was reduced to six-part series and changed to a seasonal system, and the production of Season 2 was confirmed.