While the average incarceration rate among the 40 largest counties in 2014 was 271 per 100,000 residents, the full range of rates spans Philadelphia (810 per 100,000) and San Bernardino County, California (477 per 100,000) at the high end (shaded in red), and Hennepin County, MN (134 per 100,000) and Montgomery County, MD (121 per 100,000) at the low end (shaded in blue). Counties with incarceration rates closer to the average, such as Cook County, IL (281 per 100,000) and Maricopa County, AZ (302 per 100,000), are shaded in purple.
These data were obtained through the Bureau of Justice Statistics Annual Survey of Jails (ASJ) and Census of Jails (COJ). The ASJ has been fielded 25 times between 1985 and 2014 and captures data for a sample of a few hundred jails; in 2014, the sample was approximately 800 counties, which included the 250 largest jails. The COJ has been fielded 10 times since 1970—in 1970, 1972, 1978, 1983, 1988, 1993, 1999, 2005, 2006, and 2013 - but captures data for all counties. Data for years that counties do not supply data (through the ASJ or COJ) are interpolated assuming a constant rate of change between the years when data are provided.