Mont. Code Ann. § 13-19-306
Returning marked ballots -- when -- where
13-19-306 . Returning marked ballots -- when -- where. (1) After complying with 13-19-301 , an elector or the elector's agent or designee may return the elector's ballot on or before election day by either:
(a) depositing the signature envelope in the United States mail, with sufficient postage affixed; or
(b) returning it to any place of deposit designated by the election administrator pursuant to 13-19-307 .
(2) Except as provided in 13-21-206 and 13-21-226 , in order for the ballot to be counted, each elector shall return it in a manner that ensures it is received prior to 8 p.m. on election day.