Today, jails are increasingly forced to accommodate offenders with mental illness and are typically ill-equipped to care for these offenders. In examining the States of California and Tennessee, described as dissimilar but unique in their jails and counties, this study explored the prevalence of people with mental illness in jails and the provision of services, specifically diversionary programs. Diversion is the placement of mentally ill offenders in some type of mental health treatment. Surveys were distributed in November 2003 to all the county jails in Tennessee and California, utilizing the same survey instrument. Information was solicited about a number of characteristics concerning jails and jail systems which included jail characteristics (i.e. population, imprisonment rate, facilities, mental health housing, and pre-adjudicated inmates) and inmates with mental illnesses (i.e. inmates with mental illness, over 10 percent mentally ill inmates, and inmates with developmental disabilities). Tennessee and California were seen as having similar problems, but different responses. The study found that the mentally ill population within Tennessee jails is higher than California. The results indicate that the State-level differences were driven by the smaller jails. Larger jails were more likely to report higher percentages of inmates with mental illness with more comprehensive assessments completed. In addition to geographic or size differences, legislative factors had a great influence on the operation of jails, especially in California. Corrections research had continually found that jails are an inappropriate place for people with mental health problems because their illness places them at higher risk for self-harm, suicide, and victimization. An appropriate strategy is to divert mentally ill offenders from jails. Jail administrators and mental health professionals in both States have taken steps to alleviate the problems of mentally ill populations. Notes, references