Question
Is there a such thing as a hardy marigold or a perennial marigold that could survive the winter in Illinios?

Answer
Short answer: Nope.

Long answer:

Simple enough question: Is there a hardy, Perennial Marigold?

Not so fast!

Marigolds - some of which are called Tagetes among botanists - come in several dozen Annual and Perennial species.  There are in fact many that are Perennial, but only a handful are grown commercially.  Alas, none of these is a Hardy Perennial.

You can view pictures and descriptions of these lesser known, non-hardy Perennial Tagetes at the Moutain Valley Growers website (www.mountainvalleygrowers.com/taglemonii.htm).

The Purdue University Cooperative Extension posts an entire page of "Novel Annual and Perennial Tagetes" (www.hort.purdue.edu/newcrop/proceedings1996/v3-546.html).

Ah, but one of the problems here is that in some regions of the country, a Rose is not a Rose, a Marigold is not a Marigold.  

Sure, where I come from, Long Island gardeners will be talking about Tagates when they discuss Marigolds.  But in your part of the country, maybe you're asking me about Calendula.

Unlike the Tagetes species, which seems to have been invented somewhere south of Zone 8 and below - toward the Equator - Calendula comes from the Mediterranean and East toward Asia.  The British seed purveyor, Thompson & Morgan, sells seeds for "Pot Marigolds", Calendula officinalis.  But that species is a Hardy Annual.  

Close but no cigar.

Illinois being one of the much colder parts of the country, we cannot even hope for a microclimate that will deliver Perennial behavior in the Zone 8-comfortable, tender Tagetes.

Now, if you would like to elaborate on the reasons you want to grow a Perennial Marigold - annual Tagetes are not good enough? - perhaps I can steer you in a more enthusiastic direction.  Just let me know.