AreaVibes reveals the best places to live in Illinois for 2016 using our Livability Score. The Livability Score for each city in Illinois is calculated out of 100 from a unique algorithm based on various metrics, including: amenities, cost of living, crime, education, employment, housing and weather. Illinois has a population of 12,823,860 and a population density of 222.3 people per square mile. The capital city is Springfield and the largest city in Illinois is Chicago. To filter the results, use the dropdown options to sort by population or category.