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. Create your Illinois sublease agreement, and sublet your property.Rent your unit to a subtenant with a sublease agreement form. 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. This resource provides an example of what a sublease in Illinois looks like. Download. A sublease agreement is a rental contract used for rerenting a currently leased unit to a new tenant. In Illinois, subleasing laws rely heavily on tenant agreements and cityspecific regulations. The best way to modify Application for Sublease - Illinois online. Illinois Sublease Agreement is a document between a tenant and a subtenant whom agrees to rent the same property. Landlords may ask people to fill out a rental application form and pay an application fee when applying for an apartment.