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!