A sublease agreement is a rental contract used for rerenting a currently leased unit to a new tenant. Create a sublease agreement to legally sublet your property.Our sublease contract template allows a tenant to rent a unit to a subtenant. 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. Download Illinois Sublease Agreement template, modify and send for signing using BoloForms Signature. Writing a sublease agreement. Here's a sample letter for when you give notice on your rental. An Illinois sublease agreement allows a tenant to rent out their leased property, partially or in full, to another tenant. A sublease agreement is a real estate contract for the renting of an entire apartment or bedroom between a tenant and sub-tenant. In cases where subleases are allowed, all of the provisions must be identical to the master lease.