Stumbled on this today. I noticed a house with an address of 2102 S. Avers. Next door to the north and I mean right next door, the house address is 1958. Google mapped around the area and lo and behold, couldn’t find a 20th. If I had one handy, Rand McNally would probably tell me the same.
Sometime around 1868, east-west streets on the South Side were given numbers, starting with 12th. What was previously known as Bridge Street became 20th Street. Then when the Brennan system was set up in 1909, tying house numbers to street numbers, they didn’t rename those existing streets. That meant that the first couple of miles on the South Side have more numbers than are needed for conventional 660-foot-long (eight-to-the-mile) Chicago blocks. There’s no 10th, either.
But complicating matters, 20th was renamed Cullerton at some point. So the situation will change from section to section across the city. In some places there may be both a Cullerton and a 21st, or even a 21st Place. In others, it will skip directly from 19th to 21st.
Also interesting to me was that the Avers addresses mentioned in the OP that changed from 21st to 19th did not have a street to cross for the address street number to change. The street address changed from one door to the next. :eek: