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 September 25, 2026.
Union City, California, in Alameda County, has about 66,000 residents (2024 Census Bureau estimate). A person kept in custody after an arrest in Union City is held at the county jail, run by the Alameda 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: Union City public records, Alameda County inmate search, Union City arrest records, Union City warrants, Union City criminal records, Union City court records, California arrest records and California inmate search.
Finding Someone in Custody in Union City
The county jail, run by the Alameda County Sheriff's Office, holds everyone kept in custody after an arrest in Union City, from every agency.
SearchSystems opened and checked the custody page of the Alameda County Sheriff's Office at acgov.org/sheriff_app (page title: Inmate Locator), 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 Alameda County Jail by the Numbers
On an average day in 2025 the jail held about 1,450 people, down from about 2,530 in 2019. Its rated capacity in 2023, the last year with a capacity figure, was 3,485 beds, and it ran at 50 percent of it that year. The figures are from the Vera Institute of Justice's Incarceration Trends data.
Alameda County has about 1.6 million residents (2024 Census Bureau estimate), so the jail holds about 9 people for every 10,000 residents.
Who Books People Into the Alameda County Jail
The Alameda County Sheriff's Office and the agency that reports for Union City (filed by the FBI as Union City Police Department) make the arrests that end in a booking in and around Union City.
The FBI's agency list also places six state police units, three other agencies, one state agency and three campus police departments in Alameda County (the arrest records guide names each one).
The largest arrest counts reported to the FBI were Oakland's 5,383 for 2023, the Alameda County Sheriff's Office's 2,610 for 2025 and Berkeley's 2,111 for 2025.
Together, the 13 agencies in Alameda County with all twelve months of 2025 on file reported 14,194 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 Union City arrest records.
From the Jail to State Prison
A sentence of more than a year is served in state prison, not the jail; the California Department of Corrections and Rehabilitation lists its inmates at cdcr.ca.gov/search.
Frequently Asked Questions
How do I find an inmate in Union City?
Look on the custody page of the Alameda County Sheriff's Office at acgov.org/sheriff_app. It covers people booked into the county jail.
How many people are in the Alameda County jail?
About 1,450 on an average day in 2025, the latest year in the Vera Institute's jail data, against a rated capacity of 3,485 beds.
Where do people sentenced to prison in Alameda County go?
To a facility of the California Department of Corrections and Rehabilitation; its inmate locator is at cdcr.ca.gov/search.
Is this the official Union City 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.