Mont. Code § 7-12-2108
Whenever a contemplated work or improvement, in the opinion of the board of county commissioners, is of more than local or ordinary public benefit or whenever, according to the estimates furnished by the county surveyor or the engineer, the total estimated cost and expenses thereof would exceed one-half of the total assessed value of the lots and lands assessed (if assessed upon the lots and lands fronting upon such proposed work or improvement according to the valuation fixed by the last assessment roll whereon it was assessed for taxes), the board may make the expense of such work chargeable upon the lots and lands fronting upon such proposed improvement and upon other lots and lands not fronting on the improvement and which the board shall declare, in its resolution of intention, to be the property benefited by said work or improvement and to be assessed to pay the cost and expense thereof.
§ 7-12-2108, MCA