Except in the case of the first boards and when vacancies occur before the expiration of a term, park district commissioners shall be elected without party designation at the same time and in the same manner as county commissioners. In single county park districts the three commissioners at large shall be elected by all the qualified voters in the park district while the successors in office to the four commissioners representing the four election districts, whether appointed, candidates for election or elected, must reside when appointed or elected and while serving, in the election district which they represent and shall be elected by the qualified voters residing in such district. Park district commissioners shall be elected for terms of four years or until their respective successors are elected and qualify, except where a commissioner is being elected to finish out an unexpired term when election shall be for the balance of such term. Vacancies resulting from the death, resignation or removal of a commissioner shall be filled by appointment by the board of county commissioners, such appointment to be effective only until the first Monday in January following the next general election or until a successor has been elected and qualifies for office. The four commissioners representing the election districts shall be elected at the first primary and general elections after the activation of the district and each four years thereafter and the commissioners elected at large shall be elected at the second primary and general election after such activation and each four years thereafter. The terms of elected commissioners shall commence on the first Monday in January following their election.