Mont. Code § 19-18-107
A firefighter who has vested rights in a disability and pension fund maintains prior vested rights in the fund upon its transfer to a consolidated county municipality. A disability and pension fund established as required by law in a city or town of the county prior to the election and qualification of a commission under Title 7 or other acts of consolidation or disincorporation shall be continued as one such fund for the fire department of the municipality, subject, however, to the prior vested rights of firefighters employed by any fire department established as required by law in a city or town of the county prior to the election and qualification of a commission under Title 7 or other acts of consolidation or disincorporation. The board of trustees of the disability and pension fund shall continue as provided in 19-18-104. Except as provided in this section, the disability and pension fund shall be continued and administered in the manner prescribed by law for such funds.
§ 19-18-107, MCA