Legal Question in Construction Law in Illinois

You should probably select a local general contractor who is familiar with the requirements, and let them know of this "historic" situation. A reputable local contractor would or should know what kind of windows will be acceptable. There is a special form that has to be submitted; you can find it on line in the Aurora website (you may have to apply for an on line account if you don't have one to even gain access to view it) - it's called an "HISTORIC DISTRICT/LANDMARK CERTIFICATE OF APPROPRIATENESS - APPLICATION FORM" and if you look at the top of page 2 you'll see two check-box areas. It appears that as long as the new windows will be NON-structural (ie won't require any structural modifications to the home like window rough openings and the contractor would know this) and/or will NOT reduce any required egress (the contractor also will know if so) this may be the only permit you need according to the form. If the contractor requires that you file the application, you'll need to make sure first that the windows you want to use as replacements will meet the code requirements - again something a reputable window contractor would know. And it may not be a "window" contractor, but a general contractor who is local.