St. Mary's, officially named the Municipality of the District of St. Mary's, is a district municipality in Guysborough County, Nova Scotia, Canada.

Statistics Canada classifies the district municipality as a municipal district.

The district municipality occupies the western half of the county and its administrative seat is in the village of Sherbrooke.

In the 2021 Census of Population conducted by Statistics Canada, the Municipality of the District of St. Mary's had a population of 2,161 living in 1,047 of its 1,538 total private dwellings, a change of -3.2% from its 2016 population of 2,233.

The district municipality is divided into seven electoral districts for municipal representation: