Hat tip to RedEye Royalty for its recent article on the Encyclopedia of Chicago, about which I did not know. It’s apparently been revamped recently and is available at http://www.encyclopedia.chicagohistory.org/.
You can do a keyword search, browse entries alphabetically, look at maps (TONS of maps), check out the special features, or go through the user’s guide. I did a search for baseball and got 65 results, from Baseball to Year Page: 1919. I’d also like to note that while the entry for the White Sox was on the first page of results, the Chicago Cubs does not appear in the results at all?? That can’t be right. I see Wrigley Field is on the first page.
Anyway, encyclopedia results vary between a terse few paragraphs (“Ring Lardner and Chicago Sports Reporting”) to multiple pages with integrated photographs (“Creation of Chicago Sports”). There are some crosslinks embedded within entries but not as many as I would have thought. Some results are just photographs, with plenty of tools for zooming, panning, etc. (I was able to get seriously close up on a 1915 Charles Comiskey baseball card.)
If you’re not interested in searching I recommend the special features as a good way to get acquainted with this site. The Plan of Chicago takes a deep and multipart look at city planning, while How Chicagoans Remember Their History looks at touchstones of Chicago history in local and popular culture. The Dictionary of Leading Chicago Businesses (1820-2000) is an alphabetical list (with associated entries for the most part) of notable Chicago businesses, from AMR Corp. to Zenith Radio Corp.