BJS periodically conducts census data collections from all local jails in the United States. The most recent Census of Jail Inmates was conducted in 2005. In years between census collections, BJS conducts the Annual Survey of Jails (ASJ). The survey collects data annually from a sample of local jails and uses the data to estimate the number and characteristics of inmates in local jails nationwide.

The U.S. Census Bureau, survey collection agent for the 2006-2011 ASJ, drew a sample of jail facilities from 875 local jail jurisdictions, based on information from the 2005 Census of Jail Inmates. Local jail jurisdictions included counties (parishes in Louisiana) or municipal governments that administered one or more local jails. The ASJ sample included all jails with certainty that were operated jointly by two or more jurisdictions (also referred to as multi-jurisdictional jails). Other jail jurisdictions included with certainty were—

• those that held juvenile inmates at the time of the 2005 Census of Jail Inmates and had an average daily population of 500 or more inmates during the 12 months ending June 30, 2005; and
• those that held only adult inmates and had an average daily population of 750 or more.

The remaining jurisdictions were stratified into two groups: jurisdictions with jails holding at least one juvenile on June 30, 2005, and jails holding only adults on that date. Using stratified random sampling, jail jurisdictions were selected from eight strata, based on the two conditions described above, and from four strata, based on the average daily jail inmate population during the 2005 Census of Jail Inmates.

See Methodology in each report for details specific to the collection in the Prison and Jail Inmates at Midyear series.Prison and Jail Inmates at Midyear series.

*For methodologies prior to the 2006 ASJ, please refer to the National Archives of Criminal Justice Data located at <http://www.icpsr.umich.edu/NACJD/index.html>. 

The questionnaire is modified periodically in order to capture information on evolving issues in criminal justice and topics of the greatest interest to users. Future modifications include enhancing our data collection instrument in an effort to address issues related to admissions and releases of inmates, inmate length of stay in jail, jail capacity and crowding, staff workload, and medical, mental health, and substance abuse treatment issues.