Time is computed according to the Gregorian or new style, and January 1 in every year passed since 1752 or to come must be reckoned as the first day of the year.
Mont. Code Ann. § 1-1-302
Computation of time -- what calendar used
En
Official source: Montana Code Annotated (Montana Legislature). Reproduced from public-domain Montana statutes; confirm against the official source for the current text. Not legal advice.