Reviewed and updated October 7, 2026 by the SearchSystems.net editorial team. The arrest counts are the ones each agency reported to the FBI, as the FBI held them on October 8, 2026. The jail figures are from the Vera Institute of Justice's Incarceration Trends data. Every office link was opened and checked against the office's own site between September 23, 2026 and September 25, 2026.
Chicago, Illinois, in Cook County, has about 2.7 million residents (2024 Census Bureau estimate). A person kept in custody after an arrest in Chicago is held at the county jail, run by the Cook County Sheriff's Office, and the jail's record of each person held is a public record. This guide says where to look for someone in custody, what the jail holds and who books people into it.
This guide covers the search, the jail, who books people, state prison and common questions.
Related guides: Chicago public records, Cook County public records, Chicago warrants, Chicago criminal records, Chicago court records, Chicago police reports, Illinois arrest records and Illinois inmate search.
Finding Someone in Custody in Chicago
The county jail, run by the Cook County Sheriff's Office, holds everyone kept in custody after an arrest in Chicago, from every agency.
SearchSystems opened and checked the custody page of the Cook County Sheriff's Office at cookcountyil.gov/service/locate-inmate (page title: Locate an Inmate), which answered when SearchSystems opened it on September 23, 2026.
Someone booked recently shows on that page; someone cited and released at the scene, or held a few hours at a city station, does not.
The Cook County Jail by the Numbers
On an average day in 2024 the jail held about 4,790 people, down from about 5,770 in 2019. Its rated capacity in 2023, the last year with a capacity figure, was 7,084 beds, and it ran at 73 percent of it that year. The figures are from the Vera Institute of Justice's Incarceration Trends data.
Cook County has about 5.2 million residents (2024 Census Bureau estimate), so the jail holds about 9 people for every 10,000 residents.
Who Books People Into the Cook County Jail
The Cook County Sheriff's Office and the agency that reports for Chicago (filed by the FBI as Chicago Police Department) make the arrests that end in a booking in and around Chicago.
The FBI's agency list also places 14 campus police departments and 15 other agencies in Cook County.
The Elgin Police Department, the Buffalo Grove Police Department, the Deerfield Police Department and eight more are each listed by the FBI across several counties including Cook County, so their arrests are not broken out for Cook County here.
The largest arrest counts reported to the FBI were Chicago's 32,759 for 2025, the Cook County Sheriff's Office's 3,038 for 2025 and Schaumburg's 1,950 for 2025.
Together, the 100 agencies in Cook County with all twelve months of 2025 on file reported 71,187 arrests to the FBI that year. Those kept in custody were booked into the county jail; a person cited and released at the scene was not.
From the Jail to State Prison
A sentence of more than a year is served in state prison, not the jail; the Illinois Department of Corrections lists its inmates at idoc.illinois.gov/offender/inmatesearch.html.
Frequently Asked Questions
How do I find an inmate in Chicago?
Look on the custody page of the Cook County Sheriff's Office at cookcountyil.gov/service/locate-inmate. It covers people booked into the county jail.
How many people are in the Cook County jail?
About 4,790 on an average day in 2024, the latest year in the Vera Institute's jail data, against a rated capacity of 7,084 beds.
Where do people sentenced to prison in Cook County go?
To a facility of the Illinois Department of Corrections; its inmate locator is at idoc.illinois.gov/offender/inmatesearch.html.
Is this the official Chicago website?
No. SearchSystems.net is an independent public records guide, online since 1997. It links to the official city, county, court and state offices described above and does not hold records, charge for them or take requests.