This is a website recommended by a librarian friend of mine from my former high school. The page was originally designed for ESL students, but the sites are not written in low-level English. Check out this page:
Also, here are some websites which may help you in your search for information:
- http://www.worldatlas.com/citypops.htm
- http://www.mapsofworld.com/world-city-maps/
- http://www.theguardian.com/global-development/cities-and-development
I will add more sites as I find them. Because Wikipedia articles can be changed by anyone, they are not appropriate as original sources for your project. Do look at Wikipedia to get a general idea of your city, but then try to find other, more official sites.