Explore Chicago Collections (http://explore.chicagocollections.org/) can be used to locate archival material from the member 21 institutions of Chicago Collections. Researchers can search for the locations of physical collections that they may want to consult. They can also access digital collections. More than 100,000 images are available.
In addition to searching, it is possible to browse by topics (events, government, daily life, creativity, environments, work), names, cities, and neighborhoods.
I found information on this site which relates to my family history. For example, I found that the Chicago History Museum has the Chicago Typographical Union No. 16 records. My great-grandfather Henry Brown Gatlin was a member of Chicago Typographical Union No. 16. In 1922, he was one of two members to be on the arbitration board, which selected the chairman for wage negotiations. By 1929, he worked as a business agent for the union.The Chicago History Museum also has a Chicago Mercantile Exchange album. My paternal grandfather Henry Cornelius Gatlin was a member of the Chicago Mercantile Exchange, and also served as director and officer. I also found two photos of the Chicago Mercantile Exchange Center. The first and second photos were taken from different angles. There are also photos of the Illinois State Penitentiary at Joliet, Illinois. My great-grandfather's brother William D. Gatlin was there from 16 October 1917 to 23 September 1919, when he was shot after he tried to attack a prison guard.
If you have ancestors who lived in Chicago, this site is worth a look!