Idaho Code § 15-7-101

The trustee of a trust having its principal place of administration in this state shall register the trust in the court of this state at the principal place of administration. Unless otherwise designated in the trust instrument, the principal place of administration of a trust is the trustee’s usual place of business where the records pertaining to the trust are kept, or at the trustee’s residence if he has no such place of business. In the case of co-trustees, the principal place of administration, if not otherwise designated in the trust instrument, is (1) the usual place of business of the corporate trustee if there is but one (1) corporate co-trustee, or (2) the usual place of business or residence of the individual trustee who is a professional fiduciary if there is but one (1) such person and no corporate co-trustee, and otherwise (3) the usual place of business or residence of any of the co-trustees as agreed upon by them. The duty to register under this Part does not apply to the trustee of a trust if registration would be inconsistent with the retained jurisdiction of a foreign court from which the trustee cannot obtain release.