Legal Question in Real Estate Law in Illinois

I have not seen a case like that. However, you can petition the appriopriate local authority for a waiver of setback. There may be some legal arguments, such as laches. Consult a local attorney.

With the little information you've given us, the answer I have to give is "maybe", and perhaps more than maybe. If these are platted (on the plat of subdivision, either by way of setback lines or covenants, conditions and restrictions on the plat, and all other properties on the block abide by them, the stronger the case to continue to enforce them. Since the municipality is typically (althought not always exclusively) charged with enforcing them, they often do have some leeway (up to 10%) through a process called a "variation" or "variance" procedure, but this can require notice to all affected neighbors, and some communities are more forgiving than others. You might be surprised at what people will object to. You'd think they'd just object to some huge addition; no, I've seen objections to putting air conditioning compressors in a side yard beyond the "setback line". So if you want a clearer answer, you need to contact one of us and present all the important information.