Aidan Gallagher (Five) was not allowed to be on set during any gun fight scenes because of child labor laws. Instead a body double was used.
Even though the main events of the first season take place in 2019, no character ever uses a cell phone in any episode. Public pay phones or landlines are used to communicate with other characters.
Gerard Way provided vocals for three songs featured in the show- "Happy Together" and "Hazy Shade of Winter" for Season 1 and "Here Comes The End" for Season 2.
The date that Five leaves the Academy to time-jump is November 10, 2002.