Chicago race and ethnicity data by police district

If you're trying to match Chicago police district data with the racial and ethnic makeup of those police districts, this post is for you.

The boundaries for police districts and precincts don't usually line up nicely with US census boundaries like census tracts or block groups. That makes it tough to compare incident and arrest data reported by precinct with the population of those precincts. 

But in bigger cities, census blocks are small enough to serve as atomic units that usually do fall within police precinct boundaries. So by knowing which blocks are within which districts, you can calculate the populations. Block-level data is only available from the decennial census count, so the latest data is from 2010. But it still should serve as a good measure — and a reason to fill out your 2020 census form online!

After doing these calculations for New York City, I put together Chicago's by request!

In this zip file are three data files:

chicago_2010pop_by_2020policedistricts.csv is the 2010 US Census data on race and ethnicity (just Hispanic or non-Hispanic, alas), summed by Chicago police district as those districts are drawn today — though it looks like the official map was updated last in 2018. The columns are a little cryptic, but follow the Census bureau's coding: 

  • P003001 - Total population
  • P003002 - White alone
  • P003003 - Black or African American alone
  • P003004 - American Indian and Alaska Native alone
  • P003005 - Asian alone
  • P003006 - Native Hawaiian and Other Pacific Islander alone
  • P003007 - Some Other Race alone
  • P003008 - Two or More Races
  • P005001 - Total population (again)
  • P005002 - Not Hispanic or Latino
  • P005003 - Not Hispanic or Latino: White alone
  • P005004 - Not Hispanic or Latino: Black or African American alone
  • P005005 - Not Hispanic or Latino: American Indian and Alaska Native alone
  • P005006 - Not Hispanic or Latino: Asian alone
  • P005007 - Not Hispanic or Latino: Native Hawaiian and Other Pacific Islander alone
  • P005008 - Not Hispanic or Latino: Some Other Race alone
  • P005009 - Not Hispanic or Latino: Two or More Races
  • P005010 - Hispanic or Latino
  • P005011 - Hispanic or Latino: White alone
  • P005012 - Hispanic or Latino: Black or African American alone
  • P005013 - Hispanic or Latino: American Indian and Alaska Native alone
  • P005014 - Hispanic or Latino: Asian alone
  • P005015 - Hispanic or Latino: Native Hawaiian and Other Pacific Islander alone
  • P005016 - Hispanic or Latino: Some Other Race alone
  • P005017 - Hispanic or Latino: Two or More Races

chicago_2010blocks_2020policedistricts_population.csv lists every block that's in a Chicago police district along with the district number and the data above ☝️ for each block. Note that this includes a few blocks near O'Hare airport that fall in DuPage County. The population-by-district file above is a pivot of this file.

chicago_2010blocks_2020policedistricts_key.csv is the "Rosetta Stone" of the project, which marries block numbers (as "GEOID10") with police districts. I did this using the QGIS open-source mapping software, doing some batch processing and then inspecting each district individually.

Caveats

I'm pretty confident in the process here, but did this rather quickly on a Sunday and don't have a backup editor, so there may be errors! You can check my math in the Jupyter notebooks I used.

Also, while Chicago police districts almost always follow streets — as do census blocks — there were a couple of imperfect matches:

Block 170318104003050: The northern half of this block falls in the 31st district, while the southern half falls in the 16th. A check of Google Maps shows the southern half to be almost entirely commercial, so I left it in the 31st district.

Block 17043840000204: This block in DuPage County is adjacent to O'Hare airport, and the southern portion hangs outside of the 16th district (and not into any other district). But the overhang is almost entirely a rail yard, so I left it in the 16th district.

Let me know

Tweet at me at @jkeefe if this helps you ... and especially if you find anything amiss. Also hit me up if you'd like this for data work you're doing in your city.