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 on September 23, 2026.
Mercer County, Illinois, has about 15,000 residents (2024 Census Bureau estimate). A person kept in custody after an arrest in Mercer County is held at the county jail, run by the Mercer 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: Mercer County public records, Mercer County arrest records, Mercer County warrants, Mercer County criminal records, Mercer County court records, Illinois arrest records and Illinois inmate search.
Finding Someone in Custody in Mercer County
The county jail, run by the Mercer County Sheriff's Office, holds everyone kept in custody after an arrest in Mercer County, from every agency.
SearchSystems opened and checked the jail page of the Mercer County Sheriff's Office at mercercosheriff.org (page title: Mercer County Sheriff, IL), phone (309) 582-5194, 906 SW 3rd St. Aledo, IL 61231, which answered when SearchSystems opened it on September 23, 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 (309) 582-5194.
The Mercer County Jail by the Numbers
On an average day in 2019 the jail held about 59 people. Its rated capacity in 2019 was 67 beds, and it ran at 88 percent of it that year. The figures are from the Vera Institute of Justice's Incarceration Trends data.
Mercer County has about 15,000 residents (2024 Census Bureau estimate), so the jail holds about 39 people for every 10,000 residents.
Who Books People Into the Mercer County Jail
The Mercer County Sheriff's Office and the agencies that report for Aledo and Viola make the arrests that end in a booking in Mercer County.
The Alexis Police Department is listed by the FBI across two counties including Mercer County, so its arrests are not broken out for Mercer County here.
The largest arrest counts reported to the FBI were Aledo's 11 for 2025, Viola's 0 for 2020 and the Mercer County Sheriff's Office's 0 for 2020.
Aledo reported 34 arrests to the FBI for 2024. 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 Mercer County arrest records.
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 Mercer County?
Ask the Mercer County Sheriff's Office at (309) 582-5194; its jail page SearchSystems verified is at mercercosheriff.org.
How many people are in the Mercer County jail?
About 59 on an average day in 2019, the latest year in the Vera Institute's jail data, against a rated capacity of 67 beds.
What is the phone number for the Mercer County jail?
(309) 582-5194, the number on the page of the Mercer County Sheriff's Office SearchSystems verified.
Where do people sentenced to prison in Mercer 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 Mercer 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.