As of 2021, the city of Chicago has a population of 2.7 million, and for fans of the One Chicago cinematic universe, it sometimes feels like the cast of three shows — “Chicago Fire,” Chicago Med” and “Chicago P.D.” — has gone big (via Chicago Sun Times). With all the crimes, fires, and medical emergencies that occur in each of the three shows, it makes sense that there should be a large cast of characters.

Over the years, the One Chicago universe has seen many changes and upheavals, including the killing off of major characters to keep things interesting. The season three premiere of “Chicago Fire” discovered (spoiler) the show killed off Leslie Shay, played by actress Lauren German (via Us Weekly).

“Going into it, we knew if we were going to do it, it had to be someone who was going to give us a big impact, rather than choosing a lesser known character, which would have been equivalent with one punch,” “Chicago Fire” Producer Matt Olmstead told TV Line about the decision. “So instead of approaching it timidly, we thought we’d do it.”

Shay is far from the first — or last — exit from the One Chicago universe. More recently, Captain Matt Casey (Jesse Spencer) left “Chicago Fire” in a big blow, after the show’s 200th episode (via USA Today).

The departure of an actor is often followed by the arrival of a new one, which improves things, especially if the show has been on the air for a long time. In the case of “Chicago Fire,” the show recently cast Brett Dalton as Lt. Jason Pelham (via One Chicago Center). Also joining the show in season 10 is Ynez Spencer, who will replace Gallo (Alberto Rosendale) as Firehouse 51’s new recruit.

There are also some changes happening behind the camera, with executive producer Andrea Newman joining current showrunner Derek Haas as his co-showrunner (via Deadline). “Andrea’s voice is deeply imprinted in the soul of ‘Chicago Fire,’” Haas shared. “She is an incredibly talented storyteller, manager, colleague and friend. No one in Hollywood works harder or cares more about creating great television than she does. “

And fear not, “Chicago Fire” fans: The door is always open for Captain Casey to return (via USA Today). “There’s a chance I’ll come back,” Spencer said. Right now I’m still in Chicago.” “My home is here with my wife in Chicago, so I’ll still be here, but right now I’m just stepping back.”