Mont. Code Ann. § 76-1-403

When a county planning board has been established, the board of county commissioners may create a planning district that must include the property that lies outside the limits of the jurisdictional area, as established pursuant to 76-1-504 through 76-1-507 or as modified pursuant to 76-1-501 through 76-1-503 in counties where a city-county planning board has been established, as well as that property that lies outside the limits of any incorporated cities and towns. Subject to 15-10-420, the board of county commissioners may levy a tax on the taxable value of all taxable property located within the planning district for planning board purposes, under procedures set forth in Title 7, chapter 6, part 40.