Idaho Code § 5-404
In all other cases the action must be tried in the county in which the defendants, or some of them, reside, at the commencement of the action; or, if none of the defendants reside in the state, or, if residing in this state, the county in which they reside is unknown to the plaintiff, the same may be tried in any county which the plaintiff may designate in his complaint; and if the defendant is about to depart from the state, such action may be tried in any county where either of the parties reside, or service is had, subject, however, to the power of the court to change the place of trial, as provided in this code; provided, that all actions against life or fire insurance companies, suit or action may be commenced and tried in the county where the death occurred or the loss was sustained; and provided, further, that in all actions against any corporation organized under the laws of the state of Idaho, suit or action shall be commenced and tried in any county of this state where the defendant has its principal place of business or in the county in which the cause of action arose.
Idaho Code § 5-404