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Using the Census Bureau’s Advanced Group Quarters Table

by Peter Wagner, last updated July 3, 2024

Prison-based gerrymandering is the result of two related, but distinct, problems that require two separate solutions. First, the Census Bureau counts incarcerated people as residents of the wrong location (at the prison). Second, the Census Bureau fails to count incarcerated people as residents of the correct location (at their homes).

This memo concerns fixing the first half of the problem: finding the prisons in the Census data. Mathematically, counting incarcerated people at the prison location has a larger vote dilutive effect than simply failing to count them at the correct home address. This half of the problem is not only most important, it is also the most difficult for data users to fix without Census Bureau cooperation.

All of this is made more complicated by the fact that the Census Bureau publishes data not for individual addresses or institutions, but aggregated to the approximately 11 million Census “blocks.” In an urban area, a block might be a city block, but particularly in rural areas the shapes can look quite arbitrary and contain a mix of institutional and residential land.

Traditionally, the first counts of people in “group quarters,” which includes prisons, are not available until the summer of the year after the Census when a file called Summary File 1 is published. The Prison Policy Initiative uses these data to calculate the electoral impact of prison-based gerrymandering, but these data have has historically been published too late to be useful during redistricting. In 2000, even if states were aware of the problems caused by prison-based gerrymandering, they would have been unable to correct the data; and the over 100 counties that manually removed prison populations from the redistricting data often used methods too imprecise, or incompatible with other data to be appropriate for broader use.

In decades past, states and communities that wished to avoid prison-based gerrymandering were stuck. Literally, just finding the prison populations in the redistricting data was difficult. Yes, you may know where Attica prison is in upstate New York, but the prison population is often mixed with that of nearby homes in the final Census data. Even worse, facilities are sometimes assigned to the wrong location. A common problem is a facility assigned to a location that is across the street, town, or county from its actual physical location.

While as advocates, we have long argued for the Census Bureau to count incarcerated people at their home addresses, the Census Bureau squandered the necessary planning time to make that change for the 2010 Census. But last February, the Census Bureau announced a change in its data publication schedule that will help state and local governments make their own adjustments to avoid prison-based gerrymandering, by giving them the information they need to find the prison populations within the Census counts.

For the 2010 round of redistricting, the Census Bureau will release some prison population data earlier than in past decades, as a tool to help states avoid prison-based gerrymandering in redistricting. Director Groves summarized on his blog:

“This decade we are releasing early counts of prisoners (and counts of other group quarters), so that states can leave the prisoners counted where the prisons are, delete them from the redistricting formulas, or assign them to some other locale.”

Delaware, Maryland, New York, and perhaps a few other states will be using these data in combination with their own home address data to count incarcerated people at home for redistricting purposes. These states will thus solve both of the problems outlined above; incarcerated people will not be counted at the prison location, and they will be counted at home.

An additional 100-200 counties and perhaps several states will use the Census Bureau’s advanced group quarters table alone, solving only the first part of the problem; they will adjust redistricting data in a way that avoids padding the districts that contain prison populations, but does not count incarcerated people at their home addresses.

Data structure and new release schedule

Remember: You need to know what correctional populations were counted by the Census Bureau and where those populations were counted. This is often not the same location as the prison’s mailing address, and inversely, you can’t assume that all populations counted at the prison’s address are actually incarcerated.

In early May 2011, for the first time, the Census Bureau will publish an Advanced Group Quarters Table of the block level counts of correctional facilities and other group quarters. This is the same table that will be eventually published as Table P42 in Summary File 1 in June, July and August 2011. (And it’s very similar to Table P37 produced for the 2000 Census.) But in redistricting, time matters, and having these data earlier can make big difference.

By law, the redistricting data, often referred to by the statute that required its creation, PL94-171, must be made available to the states by March 31, 2011. In practice, the Census Bureau releases it in waves starting in February. In 2010, the PL94-171 data will contain only basic information for redistricting including: total population, race/ethnicity, total population 18 or over, race/ethnicity for the population 18 and over, and housing occupancy.

Census publication Significance
Dec. 2010 - Feb. 2011
2010 Census geography Possible to start looking at where prison populations might have been counted and whether it is likely that non-prison populations are in the same blocks.
Feb. - Mar. 2011
PL94-171 redistricting data Redistricting begins. It may be worthwhile to start looking for presumed prisons in the data.
May 2011
Advance Group Quarters table Prison populations can be identified in the redistricting data. The process of determining which facilities are state, federal, or otherwise relevant can begin.
June - Aug. 2011
Summary File 1 This will be the first opportunity to fully determine race/ethnicity for the correctional population.

What you will find in the Advanced Group Quarters Table:

  • For each of the ~11 million census blocks, the number of people in:
    • Correctional facilities for adults
    • Juvenile facilities
    • Nursing/skilled care facilities
    • Other institutionalized facilities
    • College/university student housing
    • Military quarters
    • Other non-institutional facilities

The Advanced Group Quarters Table won’t have everything:

  • No home addresses of people counted in group quarters.
  • No names of facilities.
  • No indication whether each block contains one correctional facility or multiple facilities.
  • No indication of the types (prison, jail, private, etc.) of facilities.
  • No data on race/ethnicity/age (although it may be possible to compare generate close estimates of race/ethnicity/age immediately if the correctional population is similar to the total population of the block, and very close estimates if you can wait until your states’ Summary File 1 is available.
  • No other demographic information.

What additional information you can get from Summary File 1 available June-August 2011:

  • The types of correctional facilities (prison, jail, private, etc.) We recommend against relying on these classifications and will provide an alternative methodology.
  • Nine combinations of race/ethnicity to the tract level (larger than blocks) by 6 age/gender groups
  • Nine combinations of race/ethnicity to the block level for the “institutionalized population” with a separate ability to separate out by 3 age groups.

How and when to get the Advanced Group Quarters Table:

Recognizing that time matters, the Census Bureau decided to publish the data in the quickest way possible. The downside to this decision is that it’s not going to be in a particularly convenient format and we don’t have a specific date for its release. The Census Bureau is saying the data will be available as soon as possible, which they project to be in early May. Redistricting bodies and advocates will need build their timelines around having these data in early May.

The data itself will be published in a text file on the Bureau's FTP site. In addition to the block counts, there will also be state totals, state-county totals, state-county-census tract totals, and totals for various kinds of voting districts and subtotals of some of the group quarters types. In all, my rough estimate is that it will be a text file with 13 million rows and 10 columns of counts. That’s a significant amount of data that we need to process to locate approximately 5,000 correctional facilities, of which only 1,500 are state and federal prisons.

What the Prison Policy Initiative will be providing to support data users:

Our goal is to help advocates steer line drawers to avoid prison-based gerrymandering. We intend to give you the tools to be able to answer in detail these questions:

  • Do the proposed districts contain large correctional facilities?
  • What kinds of correctional facilities are in those districts?

November 2010-May 2011: Guidance on preparing your data systems for the Advanced Group Quarters table, and, where necessary, proceeding without it, including:

  • Analyzing geography, including anticipating where prisons were counted and whether non-prison populations were likely counted there.
  • What and where the Census Bureau counted correctional facilities in your state in 2000
  • Historical corrections data from 2000, and hopefully soon, 2005 and 2010, to match with the federal Census.
  • Guidance on how different types of correctional facilities in your state should be handled (i.e. jails differently than state or federal prisons?)
  • Referrals to consultants who have the necessary skills to help, including:
    • Patty Becker <>, APB Associates
    • Bill Cooper (FairPlan2020, )
    • Anthony Fairfax (CensusChannel LLC,, )
    • Howard Simkowitz (Caliper)

Early May 2011: Hopefully within hours of the Census Bureau’s release we intend to release several things that will make it much easier to use the Advance Group Quarters Table:

  • A version of the PL94-171 total population table adjusted to show the total populations without any correctional facilities. This will be available in both ESRI shapefile and a tabular form.
  • ESRI shapefiles with the advanced group quarters table for each state.
  • An online tool powered by Google Maps that shows the correctional facilities as counted by the Census in each county, and links to the same data (often annotated by the Prison Policy Initiative) from 2000. Non-technical users have found this tool extremely easy to use, and some technical users prefer it over using GIS software.

Late May 2011 and afterwards:

  • We’ll be applying annotations to Census 2010 correctional counts to identify facilities by name and type.
  • We’ll be providing adjusted race/ethnicity calculations by counties or providing guidance on how you can calculate them yourself on an as needed basis.


The Census Bureau’s decision to release an Advanced Group Quarters table is a huge step forward that will give communities more choices about how to draw their districts.

As this articles describes, the Advanced Group Quarters table has its limitations, but with advance planning we can minimize the impact of those limitations, and draw better districts to minimize the effect of prison-based gerrymandering in this round of redistricting. In the future, we can work to convince the Census Bureau to eliminate prison-based gerrymandering by counting incarcerated people at their home addresses.

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