The individual was isolated immediately and the living unit quarantined, officials said.
Monkeypox: Everything you need to know about origin, symptoms, spread and vaccines
Contact tracing is underway and officials said the risk for the jail population and staff is low.
WATCH | Dr. Ashton weighs in on Chicago monkeypox cases
Dr. Jen Ashton weighs in on Chicago monkeypox cases
"It is important to remember that the population in the jail is a microcosm of the community," Cook County Health said.. "As such, it is reasonable to expect cases to appear within the jail. The individual is believed to have contracted the virus in the community prior to being ordered into custody at the jail."
Cook County Health and the Cook County Sheriff's Office are working with the public health departments for Chicago and Illinois as well as the CDC.
5 things to know about monkeypox and skin: Analysis
The Chicago Department of Public Health will be at the jail Tuesday to offer testing and vaccination for eligible individuals.