50 ILCS 510/6
On the basis of evaluations, discussions and presentations, the political subdivision shall, unless it has a satisfactory relationship for services with one or more firms, select no less than 3 firms which it determines to be the most qualified to provide services for the project and rank them in order of qualifications to provide services regarding the specific project. The political subdivision shall then contact the firm ranked most preferred and attempt to negotiate a contract at a fair and reasonable compensation, taking into account the estimated value, scope, complexity, and professional nature of the services to be rendered. If fewer than 3 firms submit letters of interest and the political subdivision determines that one or both of those firms are so qualified, the political subdivision may proceed to negotiate a contract pursuant to this Section and Section 7.
50 ILCS 510/6