In her story today, WBEZ reporter Odette Yousef tells how she received a tip about a Craigslist posting for an apartment in Chicago that included the language, ‘no Section 8 or minorities.’

The exclusion of minorities is a clear violation of the Federal Fair Housing Act of 1968. But the refusal of Section 8, or Housing Choice Vouchers, is also illegal. It violates Chicago’s Fair Housing Ordinance. We wanted to see how often that happens.

We decided to collect postings to the Chicago Craigslist housing section for the entire month of June. We assumed that month would have a higher number of movers and open units, and that the time period would be long enough to get a sizable sample of different types of listings. Additionally, we extended the analysis to include suburban Cook County, which has had a source of income protection similar to Chicago’s for voucher holders since 2013.

We set up a search to capture phrases such as ‘Section 8’,’ ‘vouchers’ or variations. Each day we saved all the results of the search to a database, capturing the title, body, price and location of each post.

At the end of the month we had more than 2,800 unique listings throughout the Chicago metro area. Unique in this case means a unique posting on Craigslist, not a unique housing unit. Many landlords post units multiple times, sometimes with the exact same language. We decided to keep these in the dataset, as we felt it more accurately represented what a voucher holder would have encountered while searching for housing in June.

In our database we also tagged posts as positive or negative to voucher holders, using keywords such as ‘welcome’ or ‘accepted.’ We then reviewed those to confirm the classification. We also attempted to add location information to posts that didn’t have an address or latitude and longitude coordinates.

Location proved to be a difficult problem to solve. While many posts came over geotagged, hundreds had no coordinates or address. Some had descriptions, such as a Chicago neighborhood, that allowed us to classify it as within Cook County or the city of Chicago, but not a point we could map. Those are included in the total counts for those areas, but aren’t present on our map. Listings we could not confirm a location for are included in our total counts, but not for any specific area.

Overall we found 244 listings that had language discouraging voucher holders from applying, around 9 percent of the total. That included 135 in the City of Chicago, and 96 in suburban Cook County.

See Yousef’s full report for more on why landlords are still creating ads like this, and why it typically goes unpunished.

Chris Hagan is a web producer and data reporter at WBEZ. Follow him @chrishagan.