Know anything about squatting laws in Chicago?

We found a reference to a squatting law in Chicago in an article, but it wasn’t an actual reference (ie, there was nothing noting the specific law). The article was from the ‘70s and the law had to do with squatters being able to stay as long if they were improving the property. We wanted to know what the actual law was and if it is still around, but my Google searches have been very poorly structured in terms of results (I can’t get any good ones). Anyone able to help?