(1) The commissioners shall be registered voters and residents of their respective districts.
(2) Beginning in 1992, any person seeking nomination or election to the county board of commissioners in a county having more than four hundred thousand inhabitants as determined by the most recent federal decennial census shall have resided within the district he or she seeks to represent for at least six months immediately prior to the date on which he or she is required to file as a candidate for such office. No person shall be eligible to be appointed to the county board in such counties unless he or she has resided in the district he or she would represent for at least six months prior to assuming office.
(3) This section shall be complied with within six months after a determination that the population has reached more than four hundred thousand inhabitants as determined by the most recent federal decennial census.