St. Mary is a CDP located in Glacier County, Montana. St. Mary has a 2026 population of 257. St. Mary is currently growing at a rate of 6.64% annually and its population has decreased by 0% since the most recent census, which recorded a population of 0 in 2020.
The median age in St. Mary is 25.8 years: 25.5 years for males, and 43.3 years for females. For every 100 females there are 127.1 males.
Data after 2023 is projected based on recent change
Overall: 25.8 years
Female: 43.3 years
Male: 25.5 years
There are 173 adults, (14 of whom are seniors) in St. Mary.
Female: 85 (44%)
Male: 108 (56%)
The racial composition of St. Mary includes 62.18% White, 15.03% other race, 12.44% Native American, 10.36% Native Hawaiian or Pacific Islander, and smaller percentages for and multiracial populations.
| Race | Population ↓ | Percentage (of total) |
|---|---|---|
| White | 120 | 62.18% |
| Other race | 29 | 15.03% |
| Native American | 24 | 12.44% |
| Native Hawaiian or Pacific Islander | 20 | 10.36% |