Don't bother with the board of review.
Hire an attorney specializing in property tax reduction in Cook County. The process is as follows (defined by law). First you can supply your proof and numbers to the township assessor for consideration. They rarely do anything. Then, appeal at the board of review. There is a reappeal step there as well. Then, appeal in front of PTAB. Then, if you still think you have a case you can file a lawsuit with your proof to challenge the assessment.
If your purchase price is lower than the market value given by the assessor talk to the assessor and see if he/she will accept that price as fair market value and make that a condition of your purchase contract.
Oct 14, 2012