BJS periodically conducts census data collections from all local jails in the United States. 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 2006–2014 ASJ, drew a sample of local jail jurisdictions, based on information from the 2005 Census of Jail Inmates. Local jail jurisdictions include counties (parishes in Louisiana) or municipal governments that administered one or more local jails. The ASJ sample includes 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
• 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. The sampling design used for the 2014 ASJ is the same as the design used for the 2013 ASJ. The 2013 ASJ differed from the 2006–2012 ASJs in that it included in the sample, with a probability of one, all California jail jurisdictions in response to the two enacted laws—AB 109 and AB 117 by the California State Legislature and governor—to reduce the number of inmates housed in state prisons starting October 1, 2011. The inclusion of all California jail jurisdictions resulted in an additional 21 jail jurisdictions (for a total sample size of 891 jurisdictions). Since the enactment of the two laws in recent years, the California jail population has experienced changes in size that cannot be compared to the changes of any other state in the United States. For this reason, the California jail jurisdictions were put in separate strata so that they could represent only California jurisdictions. The same sampling design was adopted for the California jurisdictions.

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

*For methodologies prior to the 2006 ASJ, refer to the National Archive of Criminal Justice Data. 

The questionnaire is modified periodically 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.