Information on Chicago's population, birth and death rates, immigration and emigration rates, age distribution, and population growth rates
The most current census is from 2006
Here is the information I found for 2005 and 2006
Population in 2005 according to the Chicago census report was 2,842,518. In 2006, the population was just over 2.7 million - so I would use the information from 2005.
If you use this link, it's from Chicago's census for 2006 - it's a fact sheet giving you all the information you ...
Information on the demographics and populations of Chicago based on the most recent census. The census is attached through the website provided.