Before founding Promise City, Collier had already begun to recruit residents. He had gathered together many P-positives, who had lived together in an isolated small town until they were discovered by Tom Baldwin. Since they were no longer safe from NTAC, the residents were uprooted, and led by Collier to found Promise City.
The area claimed by Collier started as just a run-down, highly polluted part of the South side docks of Seattle, WA. A square mile of the city is cordoned off with glowing devices that cause intense pain when approached. NTAC quickly discovers Collier's actions due to a vision by Maia Skouris of their location. Collier announces that he welcomes any P-positives in Promise City, but warns that there will be consequences if the government interferes. He uses film crews to record the benefits his people are doing, like removing pollution from the water. He tries to demonstrate that with combined efforts of P-positives, even formally undesirable land can once again sustain life. Despite Collier's warnings, the government sends in P-positive soldiers from their enhanced soldier program to try to put an end to Promise City. Their attempt is unsuccessful, and as a result Collier expands the boundaries of Promise City to double its size.
The residents remain at odds with the government until the outbreak of the Promicin virus starts killing thousands of people. With all of Seattle in panic and anarchy, Kyle Baldwin offers the government the use of his people (immune to the virus, due to already being P-positive) to restore order. Having no other options, NTAC accepts help from the residents from Promise City, while worrying that they will not relinquish control over the city after the incident. After the outbreak is contained, Collier instead expands the borders of Promise City to now encompass all of Seattle. His proclamation is received by cheers from the residents of Seattle, now largely P-positive themselves, with over 9,000 new people with abilities.
This group is later expanded to include all the residents of Seattle.
Though the characters claim that the location is on the Duwamish River delta, the map used and the footage featuring Promise City makes it clear this is impossible. The commentary states that Promise City was shot in Vancouver, British Columbia, Canada (presumably somewhere in the Burrard Inlet).