St. Marys: Demographics & People
St. Marys is home to 96 people, in 44 households. Population shrank 14.3% from 112 (2022) to 96 (2024). Median age 55.5 years. (16.7y older than Warren County; 16.7y older than Iowa). Children under 18 are 3% of the population. Population is 98% White (non-Hispanic). The community is relatively homogeneous (Simpson index 0.00). 64% of households are family-led. County is gaining 2,677 residents per year (2022-2023). County health: 42% adult obesity, 17% smoke.
- 2.2 people per household.
- 36% non-family households (singles, roommates).
Population & Trend
Population shrank 14.3% from 112 (2022) to 96 (2024). Estimated 2026 population: ~82 (extrapolated at -7.1%/yr trend). Census Bureau Vintage estimate: 66.
| Census data vintage | 2024 |
|---|---|
| Population | 52,403 people |
| Annual growth rate · Population change | -14.3% |
| Annual growth rate · Population (2022) | 112 |
| Annual growth rate · Population (2024) | 96 |
| Annual growth rate · Trend category | shrinking |
| Population | 96 people |
| Population Estimate | 66 |
Sources: Census ACS 5-Year 2023, Table B01003 · Refreshed 2026-04-12
Age Distribution
Median age 55.5y is 16.6 years older than the U.S. median (38.9y). Children under 18 make up 3% — below the U.S. share of ~22%.
| Age Summary · Median age | 55.5 years (vs Iowa 38.8y) |
|---|---|
| Age Summary · Children Pct | 3.1% |
| Age Summary · Character | retirement community |
| Population under 18 | 3 |
| Median age | 55.5 years (vs Iowa 38.8y) |
Sources: Census ACS 5-Year 2023 · Refreshed 2026-04-12
Race, Ethnicity & Diversity
Of 96 residents, race / ethnicity breaks down by Census ACS counts (a person can identify with one or more groups). The Simpson diversity index is 0.00 (0 = single group, 1 = perfectly even distribution); this is read as relatively homogeneous.
| White residents | 112 |
|---|---|
| Diversity Index · Diversity label | relatively homogeneous |
| Diversity Index · Groups counted | 1 |
| Diversity Index · Largest group share | 100.0% |
| White (non-Hispanic) population | 97.9% |
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 (4)
Citizenship & Origin
Where residents were born and their citizenship status (Census ACS).
| Residents born in this state | 74 |
|---|---|
| Residents born in another state | 20 |
| Share born in this state | 77.1% |
| Share born in another state | 22.9% |
| Native-born U.S. citizens | 20.8% |
| Naturalized citizens | 2.1% |
| Total foreign-born residents | 3 |
| From Europe | 3 |
Households & Family Composition
44 households. Averaging 2.1 people each — smaller than the U.S. average of 2.5. 64% are family households — near the U.S. share of ~65%. Of 32 families, 16% are married couples with children.
| Children under 18 | 10 |
|---|---|
| Total families | 32 |
| Married couples with children | 5 |
| Average household size | 2.15 |
| Women who gave birth (past year) | 19.0% |
| Grandparents living with grandchildren | 357 |
| Grandparents responsible for grandchildren | 86 |
| Family households | 28 households |
| Households that are families | 63.6% |
| Total households | 44 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. 3.1% moved within the county in the past year — the U.S. baseline is roughly 8–10%. The surrounding county is gaining 2,677 residents per year on net (IRS migration data).
| Lived in same home a year ago | 96.0% |
|---|---|
| Moved within the county (past year) | 3.1% |
| Migration · People moving in (annual) | 56,353 |
| Migration · People moving out (annual) | 53,676 |
| Migration · Net migration (in − out) | 2,677 |
| Migration · Population growing | Yes |
| 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 | 2 |
|---|---|
| Disability rate | 1.5% |
Other
| Congressional District · District | 1 |
|---|---|
| Congressional District · Formatted | IA-01 |
| Congressional District · Congress | 118th |
| Cdc Birth Rate · Fips | 19,181 |
| Cdc Birth Rate · State Fips | 19 |
| Cdc Birth Rate · County Fips | 181 |
| Cdc Birth Rate · County | Warren |
| Cdc Birth Rate · Birth Rate | 7.5% |
| Cdc Birth Rate · Lower Ci | 5.90 |
| Cdc Birth Rate · Upper Ci | 9.40 |
| Cdc Mortality · Fips | 19,181 |
| Cdc Mortality · County | Warren County |
| Cdc Mortality · Urban Rural | Medium metro |
| Cdc Mortality · Total Deaths 2020 2023 | 1,164 |
| Cdc Vaccination · Fips | 19,181 |
| Cdc Vaccination · County | Warren County |
| Cdc Vaccination · Dose1 Pop Pct | 66.7% |
| Cdc Vaccination · Series Complete Pct | 61.9% |
| Cdc Vaccination · Booster Pct | 59.3% |
| Cdc Vaccination · Population 2019 | 51,466 |
| Cdc Vaccination · Metro Status | Metro |
| Family Score · Score | 6.50 |
| Family Score · Schools | 11 |
| Family Score · Children Pct | 3.1% |
| Family Score · Rating | good |
| Town Summary · Key Facts | population 96, shrinking, retirement community, upper-middle, blue collar |
| Town Summary · Population | 96 people |
| Town Summary · County | Warren County |
Sources: Census place-to-CD118 crosswalk (place_fips) · federal dataset cascade