The school featured in All Of Us Are Dead is called Hyosan High School and wasn't filmed at an actual school. The building was constructed just for the series.
Based on the webtoon "Now at Our School (Jigeum Woori Hakkyoneun)" by Joo Dong-Geun (published from May 13, 2009 to November 2, 2011 via Naver Webtoon Corp.).
In the show they refer to a popular Korean Zombie movie: Train to Busan.
In the U.S.A the Emergency Services number is 911. In South Korea, it's reversed, 119.