County officers of each county may organize for themselves a State association as follows:
(1) County commissioners, with the county solicitor, the chief clerk to the county commissioners and officers who are counterpart personnel in counties having a home rule charter or optional form of government.
(2) County controllers.
(3) Sheriffs.
(4) District attorneys.
(5) Probation officers.
(6) Registers of wills and clerks of orphans' courts.
(7) Prothonotaries and clerks of courts.
(8) County treasurers.
(9) Recorders of deeds.
(10) Directors of veterans' affairs.
(11) Coroners.
(12) Jury commissioners.
(13) County auditors.
(14) Public defenders.