The four cities in Illinois that are represented in the crossword solutions are Decatur, CAIRO, Peoria, and Elgin. Decatur is a city located in Macon County in central Illinois, with a population of over 76, 000 people. CAIRO is a city located in Alexander County in southern Illinois, with a population of around 2, 800 people. Peoria is a city located in Peoria County in central Illinois, with a population of over 115, 000 people. Elgin is a city located in Kane County in northern Illinois, with a population of over 110, 000 people.