Idaho Code § 40-1602: Petition.

Whenever electors of a portion of the territory embraced in any existing highway district desire that their portion be detached from the highway district, a petition describing the territory by its boundaries, signed by not less than twenty-five (25) electors qualified to vote at a highway district election and residing in the territory sought to be detached shall be presented to the commissioners of the county where the greatest portion of the highway district is located.