The jail is located inside the St. Louis County Justice Center at 100 S. Central Avenue in downtown Clayton.
Employees were evacuated from the facility before 10:30 a.m., but inmates were kept inside while authorities searched the building. St. Louis County Prosecuting Attorney Bob McCulloch confirmed his office had been evacuated due to the bomb scare.
Employees were allowed back in the building around 11:25 a.m. after given the all clear.
Inmates are housed on the fourth through seventh floors of the building. The jail has a maximum capacity of 1,024 inmates, according to information on the St. Louis County Jail website.
Fox 2 News will have more information on this story as it becomes available.