Idaho Code § 31-301
The ex officio auditor and recorder of any county in this state which has heretofore been, or may hereafter be, divided by the legislature shall, upon demand in writing by the ex officio auditor and recorder of any county which has been created, in whole or in part, from the territory of such divided county, deliver to the ex officio auditor and recorder of the county so created, in whole or in part, from such territory, all record books in his custody and control relating solely to persons and property situated in such newly-created county, together with all maps and plats relating to town sites, precincts, school districts, road districts and other municipalities situated wholly within the boundaries of such newly-created county, and the originals of all chattel mortgages relating to personal property within said newly-created county, and also all tax sale certificates and other papers relating wholly to, and covering property located entirely within such newly-created county. At the time of such delivery by the said ex officio auditor and recorder of the divided county, he shall take an itemized receipt from the ex officio auditor and recorder of the newly-created county, and file and keep the same in his office as a part of the records of said divided county.
Idaho Code § 31-301