70 ILCS 805/6d

The board of a forest preserve district within a county which has a population of no more than 550,000 may trade any one or more parcels of land owned by the district for one or more parcels of land owned by one or more individuals or any public or private entity whenever the board determines the trade to be advantageous to the district. The board shall approve such trade by unanimous vote of the members of the board. No trade shall be approved by the board unless all parcels of land involved in the trade have been appraised by an MAI appraiser or a State certified real estate appraiser within one year before the date the trade is to take effect.