County News

County Explorer Updates: Visualizing County Jail Population Data

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How many people are in jail, what are the characteristics of the jail population and how do the characteristics of the jail popula­tion change from year to year?

The Department of Justice Bureau of Justice Statistics (BJS) provides some help with answering these questions. Each year, BJS releases the findings from the Annual Survey of Jails. The survey provides national numbers on the jail population.

There are more than 2,800 jail jurisdictions in the United States, and BJS sends the survey to a representative sample of these jurisdictions. Jail facilities can be administered by county governments, cities, regional authorities where two or more jurisdictions have an agreement to operate the facility, or private contractors. BJS makes available the data collected by the survey. The most recent data made avail­able to the public were collected in 2013.

Click here to access the County Explorer

NACo analyzes the BJS sur­vey data for county governments to update the County Explorer, an interactive map available for free via the NACo website. For September, the update to County Explorer includes the number of persons held in county jails for non-local law authorities and jurisdictions.

In addition to holding in­mates who are awaiting trial locally or have been sentenced to serve time in the county jail, county jails also hold inmates for federal agencies and other jurisdictions. NACo’s analysis of BJS data shows that in total, 18 percent of the inmate popula­tion confined in county jails is held for the federal government, prison authorities and other lo­cal jurisdictions.

Sixty percent of county jails confine one or more individuals for the U.S. Marshals Service, Federal Bureau of Prisons, U.S. Immigration and Customs En­forcement or other federal agen­cies. An additional 60 percent of county jails also hold inmates for their state’s corrections depart­ment. County jails hold more inmates for their states’ prisons than for federal agencies. Inmates in county jails are also held for other counties from within the state and authorities in other states.

To view the recent jails data added to County Explorer, go to and click on “Map an Indicator” on the upper left side of the screen. A menu with different categories will appear. Move the cursor over “Justice and Public Safety.” A list of options appears to the right that includes “Jails – Supervised Population by Agency.” Click an indicator that is of interest, such as the number of inmates “Held for Own State.”

This month’s update to Coun­ty Explorer follows August’s additions, which included data on jail capacity, the number of people in jail and the average daily population.

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