OMG - the largest spiders living in Chicago are almost the size of your hand!!
They are the Argiope aurantia (orb weaver):
And the dolomedes tenebrosus (dark fishing spider):
(photos above: Getty Images)
Apparently neither will come into houses, at least not in the city, but if you have a cabin in Wisconsin, you occasionally might see one inside.
Chicagoans can find both spiders in city forest preserves or in the backyard.
Illinois is home to about 800 spider species -- I live in a condo in the city and these freaky things LOVE living in the windows outside my 42nd floor unit. Freaks me out to open the windows even with screens in place!