Mont. Code Ann. § 7-2-2226

All the officers elected at said election or appointed under this part shall hold their offices until the time provided by general law for the election and qualification of such officers in this state and until their successors are elected and qualified. For the purpose of determining the term of office of such officers, the years said officers are to hold office are to be computed from and including the first Monday after January 1 following the preceding general election.