Fort Collins is an underground laboratory located in Colorado in the show. It is based off of the real city in Colorado that is on the Cache La Poudre River. The show is hinting at its CDC lab that resides there.
Fort Collins is the birthplace of the ZN1-virus and it's vaccine. Studied by Dr. Merilyn Merch and Dr. Walter Kurian in 2014 on primates under the code name "Red Death", the virus jumped to humans by infecting a lab technician named Brandon Doyle. Doyle was kept as a guinea pig and has been unable to leave the lab. Other lab workers was also kept against their will as the lab went into lockdown.
The virus somehow got out and caused the zombie apocalypse.