The board of county commissioners shall place all funds received from the sale of land, sites or structures in a special fund to be used for the purchase or construction of facilities for use by the county. All such funds may be invested by the county treasurer as directed by the board of county commissioners in state or national banks or trust companies upon insured time deposit bearing interest at a rate no less than currently being paid upon insured savings accounts in said institutions or invested in direct obligations of the United States government.