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 on September 23, 2026.
Cook County, Illinois, has about 5.2 million residents (2024 Census Bureau estimate). A person kept in custody after an arrest in Cook County 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: Cook County public records, Cook County warrants, Cook County criminal records, Cook County court records, Cook County police reports, Illinois arrest records and Illinois inmate search.
Finding Someone in Custody in Cook County
The county jail, run by the Cook County Sheriff's Office, holds everyone kept in custody after an arrest in Cook County, 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.
That page is the place to look for someone booked recently. A person cited and released at the scene, or held only a few hours by a city department, will not be on it.
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 agencies that report for Chicago, Cicero, Schaumburg, Evanston, Arlington Heights, Palatine and 112 more cities make the arrests that end in a booking in Cook County.
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
The jail holds people awaiting trial and people serving short sentences. A person sentenced to prison in Cook County serves the sentence in a facility of the Illinois Department of Corrections, whose inmate locator is at idoc.illinois.gov/offender/inmatesearch.html.
Frequently Asked Questions
How do I find an inmate in Cook County?
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 Cook County website?
No. SearchSystems.net is an independent public records guide, online since 1997. It links to the official county, court and state offices described above and does not hold records, charge for them or take requests.