See Any Chicago Address

Am I the only person who uses this valuable resource but keeps forgetting its internet location? CityNews Chicago's Property Search has a ton of data on any existing Chicago address, including year built, square footage, fire information, tax information, assessed value, usually a photo -- as well as the all-important political (excuse me, "civic footprint") information: elected representatives, precicnct, ward, police beat, community area, and judicial subcircuit. Some info dates back to 2002.

Of course, if you're trying to track Chicago folks from the 19th century, you'll want to visit the Newberry Library's Chicago Ancestors site, "tools" tab, where in addition to online city directory images from 1866, 1870, 1871, 1875, 1880, 1885, 1892, and 1900, you can use tools from the Chicago History Museum to check whether your target address has had a street name change, and how its numbering was altered in 1909.