For a city that is so filled with the history of crime, there has been little preservation of the landmarks that were once so important to the legend of the mob in Chicago. Gone are the landmarks like the Lexington Hotel, where Al Capone kept the fifth floor suite and used the place as his headquarters. But most tragic, at least to crime buffs, was the destruction of the warehouse that was located at 2122 North Clark Street. It was here, on Valentine's Day 1929, that the most spectacular mob hit in gangland history took place..... the St. Valentine's Day Massacre.
Full story here, it is a good read
http://www.prairieghosts.com/valentine.html