Idaho Code § 70-1109
The boundaries of any port district may be altered and new territory may be annexed thereto as provided in this act. Such enlarged port district may include land in one or more adjacent counties. Such territory to be annexed must be contiguous to the port district and in one (1) continuous tract, and the exterior lines thereof in all cases must follow precinct boundary lines of such county or counties, so that port districts shall include only whole voting precincts; elections to annex two (2) or more separate tracts of territory shall not be held at the same time. Such annexation may be made only upon the petition of at least ten per cent (10%) of the qualified voters of the area proposed to be annexed based upon the whole number of votes cast within the precincts included within said area proposed to be annexed, at the last preceding general election; such petition shall contain the name of the port district proposed to be enlarged, a description of the exterior boundaries of the territory to be annexed, and shall refer to this section of the act, and all persons signing such petition shall, in addition to signing their name thereon, write thereon their residence address. The petition shall be presented to the county clerk of the county or counties wherein the territory to be annexed lies.
Idaho Code § 70-1109