An Illinois residential purchase agreement is a legally binding contract between the buyer and seller of a residential property. Get a comprehensive understanding of Illinois real estate purchase and sale agreements with our indepth overview and free template.Add the names, contact details, and addresses of the required parties. 1. Enter the names of the Purchaser and Seller. Residential Real Estate Purchase and Sale Contract. (For use with Single Family Homes, Fee Simple Townhomes, or Shared Community Associations).