(a) In counties with a population more than 30,000 but less than 90,000, in each forest preserve district organized after the effective date of this amendatory Act of 1997 or in which, on the effective date of this amendatory Act of 1997, the commissioners of the district are appointed by the presiding officer of the county board under Section 3a, the commissioners shall be elected as provided in this Section, rather than appointed, beginning with the first consolidated election following the effective date of this amendatory Act of 1997. There shall be 5 elected commissioners, elected from the district at large. Each commissioner must be a resident of the district. The terms of all elected commissioners shall commence on the third Monday of the month following the month of election. No party designation shall appear on the ballot for the election of commissioners. The terms of all commissioners appointed under Section 3a in a district to which this Section applies shall expire on the third Monday of the month following the month of the first election of commissioners in that district under this Section. If before August 20, 1993 (the effective date of Public Act 88-443) in a county with a population of 30,000 or less a presiding officer of a county board appointed the commissioners of the forest preserve district and if that presiding officer has, since August 20, 1993, continued to appoint the commissioners of the forest preserve district, then those appointments made after August 20, 1993, if made in compliance with Section 3a, are validated.