The address you are looking for is not the address it was
PUBLISHED 3 SEPTEMBER 2026
Chicago renumbered every street in 1909, corrected the job in 1911, and renamed several hundred streets besides. An address copied out of an 1890 census is not the address you would type into a map today, and the house it points to may still be standing under a different number.
You find the family in the 1900 census at 472 North Avenue. You look it up, and the building there is wrong — wrong era, wrong scale, wrong side of the street from what the enumerator's route implies. Or it is a parking structure.
The address is not wrong. It has simply stopped meaning what it meant.
What happened
Chicago's street numbering grew the way the city grew: annexed town by annexed town, each with its own scheme, each starting its numbers wherever it felt like starting them. By the 1900s the same number appeared on several streets in different parts of the city, numbering ran in inconsistent directions, and a mail carrier had to know the city rather than read it.
The city adopted a unified system in 1909, keyed to State and Madison as the zero point, with a consistent 800 numbers to the mile. The conversion was done in stages and it was done imperfectly. A 1911 revision corrected a great deal of it.
Alongside the renumbering, several hundred streets were renamed — mostly to eliminate duplicates, so that one Chicago street bore one name.
The practical result:
- An address recorded before 1909 is in the old system.
- An address recorded after 1911 is in the current system.
- An address recorded between them could be either, and the source rarely says which.
Why it matters more than it sounds
Three things break, and they break quietly.
Finding the building. A pre-1909 number entered into any modern map lands somewhere plausible and wrong. Plausible is the problem — you get a result, it looks like an answer, and nothing tells you it is the wrong block.
Following a family. A family that appears at one address in 1905 and a different-looking address in 1915 may not have moved at all. Two numbers, one house. Read as a move, it invents a migration that never happened and sends the search after records in a neighbourhood the family never lived in.
Reading the neighbourhood. Half of what an address is worth to a family history is context: which parish, which school, which ward, which ethnic enclave, what the block was. All of that is tied to the physical location, and the physical location is what the wrong number loses.
How it is actually resolved
The conversion is not arithmetic. There is no formula that turns an old number into a new one, because the old system was not systematic. It is done with the published conversion tables the city and its directory publishers issued at the time, cross-checked against a source that ties the family to a place independently.
The check matters. A conversion table gives a candidate; a second source confirms it. Useful ones:
| Source | What it fixes the address against |
|---|---|
| City directories, year by year | The occupant's name, so the number is tied to a person |
| Parish registers | The parish, which pins the general location |
| Fire insurance atlases | The building itself — footprint, materials, lot |
| Census enumeration order | The neighbours, and the route the enumerator walked |
| Ward and precinct boundaries | Which political division the address sat in |
When two of those agree, the address is settled. When they disagree, that disagreement is a finding and belongs in the report — often it means the source was recorded from memory rather than from the door.
The part worth remembering
An old Chicago address is not a location. It is a piece of evidence that has to be converted before it can be used, and the conversion has to be shown rather than assumed.
If a family history hands you a street number from 1890 and a modern photograph of the building said to stand there, ask which conversion was used and what confirmed it. Quite often the honest answer is that nobody checked — and the house in the photograph belonged to somebody else entirely.
Working on a Chicago family and stuck on something like this? Start a conversation — the first one is free.