An Illinois sublease agreement is a contract in which an existing tenant (sub-lessor) and a third-party (the sub-lessee) establish a rental arrangement. The subtenant agrees to assume all of the obligations and responsibilities of the sublessor under the original lease for the duration of the sublease agreement.Simplify your subleasing process with our Chicago Sublease Agreement. Easily edit, fill and sign for free with Lumin. This resource provides an example of what a sublease in Illinois looks like. Download. Chicago law requires landlords to allow tenants to sublease their apartments if requested. Here's what else you need to know about subleasing in Chicago. Create your Illinois sublease agreement, and sublet your property. Rent your unit to a subtenant with a sublease agreement form. A sublease agreement is a rental contract used for rerenting a currently leased unit to a new tenant.