During the Civil War…the U.S. Post Office began free door-to-door delivery of mail, contingent upon numbering of houses, and house numbering became common.
However, each “division” or side of the city had its own system, and many streets were numbered from the meandering rivers or shoreline, so that house numbers on parallel streets often failed to line up neatly.
A campaign led by Edward P. Brennan resulted in a new house-numbering system by 1908, as well as to street-naming reforms. All buildings were numbered beginning at Madison and State Streets, making the business and retail heart of Chicago the center of the new system. The clean geometry of straight lines and right angles guaranteed uniformity in numbering.