Legal Question in Landlord & Tenant Law in Illinois

Hopefully you have a written lease. That should be your starting point. If not, usually the landlord is responsible for "the building" (structure, exterior, main systems) and the tenant is responsible for "the premises" (ordinary maintenance and repairs and keeping the inside clean) but it can vary. However, if there is damage on the exterior and the tenant denies having caused it, then just because it's there doesn't make it the tenant's fault and you may have to prove it. Again, start with your lease (hopefully).