Mont. Code § 81-4-303
Any tract of land embraced within any established herd district and which contains 18 sections of government land or more, so located that at least one-fourth of the perimeter of such tract coincides with the existing boundaries of such herd district, may be excluded therefrom upon proceedings had before the board of county commissioners of the county wherein the said district has been established on a like petition, notice, and hearing and by a like order as in the case of proceedings for dissolving herd districts. When the exclusion of any such tract of land from an existing herd district is sought, the petition shall describe the tract to be excluded with common certainty and shall set forth that it is signed by the owners or possessors of 55% or more of the lands lying within the boundaries of the tract to be excluded and that less than 15% of the lands included in such tract is in actual cultivation. In any such case if the board of county commissioners at the conclusion of the hearing had shall find that the tract of land to be excluded conforms to the requirements of this section and that the allegations of the petition are true, its findings to that effect shall be spread upon the minutes and the board shall thereupon enter its order in terms that by reason of such findings and of the proceedings had upon such petition the tract of land described in the petition, which shall be further set forth with common certainty in the order, is thereby excluded from such herd district for all purposes thereafter. Forthwith upon the making and entry of any such order of exclusion the tract of land therein described shall be deemed for all purposes thereafter to be excluded from and to form no part of the herd district affected thereby.
§ 81-4-303, MCA