In 1909, street numbers changed, with a general rule of thumb that odd numbers became even and vice-versa. Madison was used as the baseline for numbering north and south while State was used as the baseline for numbering east and west.
In 1911, street numbers in the Loop changed, the area between the Chicago River and Roosevelt Road and the Chicago River and Lake Michigan.
Street names in Chicago changed over the years. The Chicago Public Library has the Street Name File, listing the origin of street names and the date names changed, in the Municipal Reference Collection on the fifth floor of the Harold Washington Library Center.
City directories will sometimes list street name changes in their front material so that dates of changes can be pinpointed. Otherwise, we have a comprehensive list without dates. A hyphen preceding an entry indicates a former street name. Its new name follows it and the coordinates refer to the new name.
There is one section of the city that is an exception to the usual guidelines for street numbering changes. If you are working with an address from a street that runs north-south and is south of Roosevelt Road (formerly 12th Street) and east of the Chicago River, that is one of the exceptions.
The numbering in this area was changed in 1879 to match up with the numbered streets on the South Side—i.e., 2200 S. Prairie would be at the intersection of 22th Street and Prairie Avenue. If your address is from a date after 1879, then it will be unchanged to the present.
If you have a pre-1879 address, that’s more complicated. There isn’t a table to show exact equivalents. Often, the closest you can come is to find the block that the number was in. The city directories around this time included street guides that showed what the street number was at each intersection. For the address 1001 Prairie, you would look up Prairie Avenue in the street guide. It shows that at 22nd St, the number was 998. At 23rd, the number was 1062. So any number between 998 and 1062 would be in the 2200 block of South Prairie today.
For State Street or Clark Street, you may be able to find an exact address equivalent. There is a fire insurance map for 1868-69 that shows these streets, with street numbers, for some blocks south of 12th. On this index to the map, click on the page you want.
Sanborn Maps are also available in print at the Research Center (use blue callslips).