Illinois je savezna država SAD-a. Peta je savezna država po broju stanovnika. Najveći je grad Chicago.
Okruzi (Counties) Illinois se sastoji od 102 okruga (counties).
Najveći gradovi
GradOkrugStanovništvo 1. travnja 2000.Stanovništvo 1. srpnja 2004.ChicagoCook2.896.0162.862.244RockfordWinnebago150.115152.452AuroraKane142.990166.614NapervilleDuPage128.358140.106PeoriaPeoria112.936112.720SpringfieldSangamon111.454114.738JolietWill106.221129.519ElginKane94.48797.761WaukeganLake87.90191.602CiceroCook85.61683.102DecaturMacon81.86078.751Arlington HeightsCook76.031 75.181SchaumburgCook75.38673.346EvanstonCook74.23974.811ChampaignChampaign67.51870.306PalatineCook65.47966.401BloomingtonMcLean64.80869.282SkokieCook63.34863.965Des PlainesCook58.72056.229BolingbrookWill56.32166.206Mount ProspectCook56.26555.028WheatonDuPage55.41654.979Oak LawnCook55.24554.257BerwynCook54.01652.000Oak ParkCook52.52450.993Orland ParkCook51.07754.781Hoffman EstatesCook49.49549.823Downers GroveDuPage48.72449.302Tinley ParkCook48.40156.274NormalMcLean45.38649.287
Vidi još Popis naselja u Illinoisu
Stanovništvo Indijanci Illinois nosi svoje ime po plemenskom savezu Illinois Indijanaca, gotovo potpuno uništenih od jezerskih plemena zbog ubojstva legendarnog poglavice Pontiaca. Povremeno su ovamo navraćala i plemena Chippewa, Delaware, Fox, Kickapoo, Miami, Ottawa, Potawatomi, Sac, Shawnee, Winnebago i Wyandot.