(2) Not later than the 40th day after the formation of a district and the election of the members of the first board, the commissioners shall meet and organize, first taking and subscribing an oath of office. The commissioners first elected shall determine by lot the length of term each shall hold office as follows:
(a) The terms of two commissioners shall expire June 30 next following the first regular district election; and
(b) The terms of the other three commissioners shall expire June 30 next following the second regular district election.
(3) The board of commissioners shall fill any vacancy on the board as provided in ORS 198.320. [1975 c.782 §36; 1983 c.83 §99; 1983 c.350 §295]