"Chicagoland" covers quite a large land area. Basically it's the reach of the broadcast TV channels. Within that area you have contiguous urban sprawl with farmland encroaching on the outer 1/3.
For reference I currently live in Manhattan, IL. As the crow flies, I'm. 40-42 miles SW of Downtown Chicago. I'm basically at the crossroads of "rural" and "Suburb". If you go either South or West of me, you are fully into farm country (300-1,500 person towns with 3,000-5,000 person "big towns"). To the North and/or East you have pure suburbs.
AP is a similar distance from the Loop, but straight West. Again, basically where continuous urban sprawl finally fades into farmland. If you head North or Northwest, the sprawl creeps out a bit and flirts with the 60 mile mark.
So basically think of half a circle centered on Downtown Chicago with a 40-60 mile radius extending straight South, West, and North.
Edit: The city itself extends 15 miles South of Downtown, 13 miles North, and 9 miles West.