An Illinois residential purchase agreement is a legally binding contract between the buyer and seller of a residential property. Read about the legal terms and disclosures you must add to an Illinois real estate purchase agreement.Learn what required information you must include. Purchase and Sale Agreement. A purchase and sale agreement is a contract between a buyer and seller for transacting a property in exchange for a specific price. Get a comprehensive understanding of Illinois real estate purchase and sale agreements with our indepth overview and free template. Download an Illinois residential purchase agreement template to define buyer and seller obligations, financing, and inspections. (Seller) agrees to sell the real estate and the property described above, if any, at the price and terms set forth herein, and to convey.