Denver was one of the only cities which boasted a high percentage of people living there; being one of the last cities that still stood after the Sun Flares. Only under 50% of people were not infected by the Flare. It was located in Colorado and appeared in The Death Cure. Here, normal life seemed to take its course, with shopping malls, cabs, and coffee shops. The inhabitants were frightened of catching the Flare, avoiding any contact with others and protecting themselves with masks.
Denver had an extremely strict level of security, with Red Shirts often seen patrolling the streets, trying to discover any newly infected people. Thomas once watched a customer in a coffee shop who had apparently taken The Bliss, and saw Red Shirts take him to the city's Crank Palace. There were also bounty hunters looking for Immunes to be sold to WICKED for a high price.
Thomas and his friends flew to Denver in order to meet Hans, who could remove the Swipe from Thomas and Minho. They also met Gally, who now worked for the Right Arm, which was also stationed in Denver.
The city would eventually be caved into the Flare after the infected finally outnumbered the healthy; hundreds of Cranks broke out of the Crank Palace and invaded the city. This meant that the citizens of Denver either became infected, if they weren't before the invasion, or they managed to escape.