In IL, is everything outside of Chicago a "suburb" ?

No, not at all. Illinois is a large long state. We don’t consider everything out side of Chicago a suburb. 

Technically, no, but I am sure some people in Illinois believe Chicago and its suburban communities rule the day. Actually, I have heard the same thing said about Metro Atlanta and the rest of Georgia at an increasing rate. 

really only in the Chicago Metro area that surrounds the city of Chicago.

https://en.wikipedia.org/wiki/Chicago_metropolitan...

Suburb is a shortened form of 'suburban' and usually means a residental or mixed use part or parts of a city.

No, there are other cities that are not suburbs of Chicago and rural areas.

Until you get to farmland, yes. What else would it be? 

Maybe a 30 mile radius from downtown Chicago.

Only Northeastern IL. We call it Chicagoland. Mostly it's Cook County and the adjacent 'collar counties.' 

Only if it's within commuting distance.