Idaho Code § 31-4319
After the organization of a district, additional territory adjoining the district and not included within an already existing recreation district, whether located in one (1) or several counties, may be annexed to and included within such district by the affirmative vote of a majority of the qualified electors of such additional territory voting on the question at an election held therefor, subject to the provisions of section 34-106, Idaho Code, but such additional territory shall not be annexed to and included within such district unless such annexation and inclusion are first approved by resolution of the board of such district prior to the elections on the question of annexation. The same procedure with such modifications in the form of petition, notices, ballots, etc., as may be necessary shall be adopted as provided in section 31-4304, Idaho Code, except that no change shall be made in director's subdistricts until the next regular director's election and no appointment of any director shall be made by the board of county commissioners.
Idaho Code § 31-4319