Until the 1920s, something close to 80% of all houses in Chicago were covered by enforceable restrictive covenants preventing Black families from moving in:
https://www.chicagocovenants.com/
(I volunteered for this project, will do so again soon, and recommend it; it's super fascinating, and if you go shoot me an email).
Redlining, the practice of refusing to underwrite mortgages in predominantly Black neighborhoods, continued up through around 1970.
The entire city of Chicago is defined by these apartheid-styled racial boundaries. I live in Oak Park, across Austin Blvd. from an almost totally Black neighborhood; Oak Park exists precisely because it was not redlined, and so wealthy white families could feel comfortable buying homes there. I grew up in Beverly, where a similar border exists at around 90th and Ashland:
https://interactive.wttw.com/firsthand/segregation/mapping-c...
You can look at where all the crime is in Chicago and see a map of C and D-graded tracts today. When Uber first launched here, their service map resembled these maps as well!