Reviewed and updated October 9, 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 October 4, 2026.
Marion, Illinois, in Williamson County, has about 17,000 residents (2024 Census Bureau estimate). A person kept in custody after an arrest in Marion is held at the county jail, run by the Williamson 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: Marion public records, Williamson County inmate search, Marion arrest records, Marion warrants, Marion criminal records, Marion court records, Illinois arrest records and Illinois inmate search.
Finding Someone in Custody in Marion
The county jail, run by the Williamson County Sheriff's Office, holds everyone kept in custody after an arrest in Marion, from every agency.
SearchSystems opened and checked the jail page of the Williamson County Sheriff's Office at wcsheriff.com/corrections2.html, phone 618-997-6541, which answered when SearchSystems opened it on October 4, 2026.
That page is the office's jail information page rather than a roster, so a search for a particular person goes through the office at 618-997-6541.
The Williamson County Jail by the Numbers
On an average day in 2023 the jail held about 160 people, up from about 120 in 2019. Its rated capacity in 2023 was 244 beds, and it ran at 66 percent of it that year. The figures are from the Vera Institute of Justice's Incarceration Trends data.
Williamson County has about 67,000 residents (2024 Census Bureau estimate), so the jail holds about 24 people for every 10,000 residents.
Who Books People Into the Williamson County Jail
The Williamson County Sheriff's Office and the agency that reports for Marion (filed by the FBI as Marion Police Department) make the arrests that end in a booking in and around Marion.
The FBI's agency list also places one more agency in Williamson County: John A. Logan College (campus police).
The largest arrest counts reported to the FBI were Johnston City's 1,152 for 2025, Marion's 1,076 for 2025 and Herrin's 487 for 2025.
Together, the five agencies in Williamson County with all twelve months of 2025 on file reported 2,793 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.
The counts, agency by agency and year by year, are in Marion arrest records.
From the Jail to State Prison
The jail holds people awaiting trial and people serving short sentences. A person sentenced to prison in Williamson 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 Marion?
Ask the Williamson County Sheriff's Office at 618-997-6541; its jail page SearchSystems verified is at wcsheriff.com/corrections2.html.
How many people are in the Williamson County jail?
About 160 on an average day in 2023, the latest year in the Vera Institute's jail data, against a rated capacity of 244 beds.
What is the phone number for the Williamson County jail?
618-997-6541, the number on the page of the Williamson County Sheriff's Office SearchSystems verified.
Where do people sentenced to prison in Williamson 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 Marion 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.