Not only is the general population of inmates in county jails growing, so is the prevalence of mentally ill people within these jails. The National Alliance for the Mentally Ill and the Public Citizen’s Health Research Group discovered that roughly 7 percent of jail inmates suffer from serious mental illness. This presents a problem for jail administration because all jails are constitutionally mandated to provide at least minimum mental health or psychiatric care to detainees. The problem lies in the sheer volume of detainees that are processed each day in some jurisdictions; many lack the time and resources to even screen every incoming inmate, let alone to provide psychiatric care for them. The current study sought to interview incoming inmates at the Los Angeles County jail system in order to screen for signs of mental illness. Data on 194 females and 806 males were collected over an 8-month period and involved a clinical interview and the administration of screening tests. Results indicated that 28 percent of the females and 31 percent of the males booked into the jail system rated as at-risk on at least one of the screening criteria for mental illness. These results uphold previous studies and proclamations that the mentally ill are a pervasive population in county jails across the country. This study underscores the fact that jail administration must find a way to screen and treat mentally ill detainees.