St. Mary: Demographics & People
St. Mary's population stands at 193 people, in 52 households. Population shrank 7.7% from 209 (2022) to 193 (2024). Median age 25.8 years. (7.6y younger than Glacier County; 15.0y younger than Montana). Children under 18 are 10% of the population. Population is 53% White (non-Hispanic) and 24% Hispanic or Latino. The community is somewhat diverse (Simpson index 0.24). 27% of households are family-led. County health: 36% adult obesity, 30% smoke.
- 3.7 people per household.
- 73% non-family households (singles, roommates).
Population & Trend
Population shrank 7.7% from 209 (2022) to 193 (2024). Estimated 2026 population: ~178 (extrapolated at -3.8%/yr trend). Census Bureau Vintage estimate: 160.
| Census data vintage | 2024 |
|---|---|
| Population | 13,778 people |
| Annual growth rate · Population change | -7.7% |
| Annual growth rate · Population (2022) | 209 |
| Annual growth rate · Population (2024) | 193 |
| Annual growth rate · Trend category | shrinking |
| Population | 193 people |
| Population Estimate | 160 |
Sources: Census ACS 5-Year 2023, Table B01003 · Refreshed 2026-04-12
Age Distribution
Median age 25.8y is 13.1 years younger than the U.S. median (38.9y). Children under 18 make up 10% — below the U.S. share of ~22%.
| Age Summary · Median age | 25.8 years (vs Montana 40.8y) |
|---|---|
| Age Summary · Children Pct | 10.4% |
| Age Summary · Character | young community |
| Population under 18 | 20 |
| Median age | 25.8 years (vs Montana 40.8y) |
Sources: Census ACS 5-Year 2023 · Refreshed 2026-04-12
Race, Ethnicity & Diversity
Of 193 residents, race / ethnicity breaks down by Census ACS counts (a person can identify with one or more groups). The Simpson diversity index is 0.24 (0 = single group, 1 = perfectly even distribution); this is read as somewhat diverse.
| White residents | 162 |
|---|---|
| Hispanic or Latino residents | 27 |
| Diversity Index · Diversity index (Simpson) | 24.5% |
| Diversity Index · Diversity label | somewhat diverse |
| Diversity Index · Groups counted | 2 |
| Diversity Index · Largest group share | 85.7% |
| Hispanic or Latino population | 23.8% |
| White (non-Hispanic) population | 53.4% |
Sources: Census ACS 5-Year 2023 · Refreshed 2026-04-12
Ancestry
Self-reported ancestry from Census ACS — what residents report as their ethnic origin, separate from race. Counts can exceed population because people can list multiple ancestries.
Top (6)
Citizenship & Origin
Where residents were born and their citizenship status (Census ACS).
| Residents born in this state | 65 |
|---|---|
| Residents born in another state | 79 |
| Share born in this state | 33.7% |
| Share born in another state | 66.3% |
| Native-born U.S. citizens | 40.9% |
| Naturalized citizens | 25.4% |
| Total foreign-born residents | 34 |
Households & Family Composition
52 households. Averaging 1.6 people each — smaller than the U.S. average of 2.5. 27% are family households — below the U.S. share of ~65%. Of 8 families, 0% are married couples with children.
| Children under 18 | 15 |
|---|---|
| Total families | 8 |
| Average household size | 1.60 |
| Grandparents living with grandchildren | 1,159 |
| Grandparents responsible for grandchildren | 394 |
| Family households | 14 households |
| Households that are families | 26.9% |
| Total households | 52 households |
Sources: Census ACS 5-Year 2023 · Refreshed 2026-04-12
Residential Stability & Migration
How long residents have lived here and where they came from. 59.1% moved within the county in the past year — the U.S. baseline is roughly 8–10%.
| Moved within the county (past year) | 59.1% |
|---|---|
| Migration · People moving in (annual) | 10,092 |
| Migration · People moving out (annual) | 10,112 |
| Migration · Net migration (in − out) | -20 |
| Migration · Year | 2022-2023 |
Sources: IRS SOI Migration 2021-2022 · Refreshed 2026-04-12
Disability
Census ACS measures self-reported functional limitations — vision, hearing, mobility, cognitive, self-care, or independent-living. The U.S. baseline disability rate is about 12–13%; rates trend higher with median age.
| Residents with a disability | 13 |
|---|---|
| Disability rate | 5.4% |
Group Quarters
Group quarters are non-household living arrangements counted by the Census — college dormitories, nursing homes, military barracks, group homes, correctional facilities, and similar institutional or shared housing. 128 residents live in group quarters (66.3% of population).
| Living in group quarters | 128 |
|---|
Other
| Congressional District · District | 1 |
|---|---|
| Congressional District · Formatted | MT-01 |
| Congressional District · Congress | 118th |
| Cdc Birth Rate · Fips | 30,035 |
| Cdc Birth Rate · State Fips | 30 |
| Cdc Birth Rate · County Fips | 35 |
| Cdc Birth Rate · County | Glacier |
| Cdc Birth Rate · Birth Rate | 38.4% |
| Cdc Birth Rate · Lower Ci | 31.30 |
| Cdc Birth Rate · Upper Ci | 46.70 |
| Cdc Mortality · Fips | 30,035 |
| Cdc Mortality · County | Glacier County |
| Cdc Mortality · Urban Rural | Noncore |
| Cdc Mortality · Total Deaths 2020 2023 | 388 |
| Cdc Vaccination · Fips | 30,035 |
| Cdc Vaccination · County | Glacier County |
| Cdc Vaccination · Dose1 Pop Pct | 95.0% |
| Cdc Vaccination · Series Complete Pct | 90.2% |
| Cdc Vaccination · Booster Pct | 39.7% |
| Cdc Vaccination · Population 2019 | 13,753 |
| Cdc Vaccination · Metro Status | Non-metro |
| Family Score · Score | 9.50 |
| Family Score · Schools | 17 |
| Family Score · Children Pct | 10.4% |
| Family Score · Rating | excellent |
| Town Summary · Key Facts | population 193, shrinking, young community, high crime, heritage: German/Irish |
| Town Summary · Population | 193 people |
| Town Summary · County | Glacier County |
Sources: Census place-to-CD118 crosswalk (place_fips) · federal dataset cascade