Mont. Code Ann. § 40-1-323
If the record of the solemnization of a marriage heretofore entered into has been lost or destroyed and not known to exist, the parties may join in a written declaration of such marriage, substantially showing:
History: En. Sec. 86, Civ. C. 1895; re-en. Sec. 3632, Rev. C. 1907; re-en. Sec. 5725, R.C.M. 1921; Cal. Civ. C. Sec. 76; re-en. Sec. 5725, R.C.M. 1935; amd. Sec. 1, Ch. 276, L. 1959; R.C.M. 1947, 48-131.