Mont. Code Ann. § 13-2-304

13-2-304 . Late registration -- late changes. (1) Except as provided in 13-21-104 and subsections (2) and (3) of this section, the following provisions apply:

(a) An elector may register or change the elector's voter registration information after the close of regular registration as provided in 13-2-301 and vote in the election if the election administrator in the county where the elector resides receives and verifies the elector's voter registration information prior to noon the day before the election.

(b) Except as provided in 13-2-514 (2)(a) and subsection (1)(c) of this section, an elector who registers or changes the elector's voter information pursuant to this section may vote in the election if the elector obtains the ballot from the location designated by the county election administrator.

(c) With respect to an elector who registers late pursuant to this section for a school election conducted by a school clerk, the elector may vote in the election only if the elector obtains from the county election administrator a document, in a form prescribed by the secretary of state, verifying the elector's late registration. The elector shall provide the verification document to the school clerk, who shall issue the ballot to the elector and enter the verification document as part of the official register.

(d) An elector who registers late and obtains a ballot pursuant to this section may return the ballot as follows:

(i) before election day, to a location designated by the county election administrator or school clerk if the election is administered by the school district; or

(ii) on election day, to the election office or to any polling place in the county where the elector is registered to vote or, if the ballot is for a school election, to any polling place in the school district where the election is being conducted.

(2) If an elector has already been issued a ballot for the election, the elector may change the elector's voter registration information only if the original voted ballot has not been received at the county election office, or received by the school district if the district is administering the election, and if the original ballot that was issued is marked by the issuing county as void in the statewide voter registration system, or by the school district if the district is administering the election, prior to the change.

(3) In a federal election, an elector may register or change the elector's voter registration information after the close of regular registration as provided in 13-2-301 and vote in the election if the election administrator in the county where the elector resides receives and verifies the elector's voter registration information:

(a) prior to the close of business on the Friday before the election;

(b) between 8 a.m. and 5 p.m. on the Saturday before the election; and

(c) prior to noon on the day of the election.