Mont. Code Ann. § 10-3-607

If the seat of state government at Helena is rendered unsuitable for use in that capacity, the seat of state government may be moved to an alternate location within the boundaries of the state of Montana by proclamation of the governor. The governor shall consider other Montana cities in order of their population in the last federal census, giving consideration to available communications, office space, and other factors considered pertinent. The move of the seat of government is effective until it is again moved by proclamation of the governor or action by the legislature.