Section 62. Participants

Each  plan  shall  have  at least two municipal
  corporations  as  participants.  The  county  shall  be   one   of   the
  participants  in  a  plan.   Any contract agency or contract association
  with the  approval  of  the  county  government  and  any  other  public
  corporation  may  by  resolution of its governing body elect to become a
  participant in a plan established in the county, or, in the  case  of  a
  public corporation or contract agency or contract association located in
  more  than  one  county,  in a plan established in one of such counties;
  provided, however, that the rules and regulations  adopted  pursuant  to
  section  sixty-five  of this chapter may exclude from participation in a
  plan any type of public  corporation  or  contract  agency  or  contract
  association other than the county and cities, towns and villages.