Janesville: Demographics & People
Janesville is home to 917 people, in 361 households. Population shrank 9.4% from 1,012 (2022) to 917 (2024). Median age 47.0 years. (8.0y older than Bremer County; 9.7y older than Iowa). Children under 18 are 21% of the population. Population is 97% White (non-Hispanic) and 1% Asian. The community is relatively homogeneous (Simpson index 0.04). 78% of households are family-led. County is losing 484 residents per year (2022-2023). County health: 39% adult obesity, 20% smoke.
- 2.5 people per household (vs Iowa avg 2.4).
- 22% non-family households (singles, roommates) (vs Iowa 43%).
- 58 dependents per 100 working-age (youth + seniors / 18-64) (vs Iowa 70).
Population & Trend
Population shrank 9.4% from 1,012 (2022) to 917 (2024). Estimated 2026 population: ~832 (extrapolated at -4.7%/yr trend). Census Bureau Vintage estimate: 728.
| Census data vintage | 2024 |
|---|---|
| Population | 131,144 people |
| Annual growth rate · Population change | -9.4% |
| Annual growth rate · Population (2022) | 1,012 |
| Annual growth rate · Population (2024) | 917 |
| Annual growth rate · Trend category | shrinking |
| Population | 917 people (vs Iowa 24,827) |
| Population Estimate | 728 |
Sources: Census ACS 5-Year 2023, Table B01003 · Refreshed 2026-04-12
Age Distribution
Median age 47.0y is 8.1 years older than the U.S. median (38.9y). Children under 18 make up 21% — near the U.S. share of ~22%.
| Age Summary · Median age | 47.0 years (vs Iowa 37.3y) |
|---|---|
| Age Summary · Children Pct | 21.2% |
| Age Summary · Character | established |
| Age Summary · Total Pop | 917 |
| Age Summary · Under 18 | 194 |
| Age Summary · 18 To 34 | 141.0× |
| Age Summary · 35 To 64 | 440.0× |
| Age Summary · 65 Plus | 142 |
| Population under 18 | 194 |
| Median age | 47.0 years (vs Iowa 37.3y) |
Sources: Census ACS 5-Year 2024 — place-level B01001 query · Census ACS 5-Year 2023 · Refreshed 2026-04-29
Race, Ethnicity & Diversity
Of 917 residents, race / ethnicity breaks down by Census ACS counts (a person can identify with one or more groups). The Simpson diversity index is 0.04 (0 = single group, 1 = perfectly even distribution); this is read as relatively homogeneous.
| White residents | 1,003 |
|---|---|
| Hispanic or Latino residents | 22 |
| Diversity Index · Diversity index (Simpson) | 4.2% |
| Diversity Index · Diversity label | relatively homogeneous |
| Diversity Index · Groups counted | 2 |
| Diversity Index · Largest group share | 97.9% |
| Asian population | 1.1% (vs Iowa 1.9%) |
| Hispanic or Latino population | 0.4% (vs Iowa 5.6%) |
| White (non-Hispanic) population | 97.4% (vs Iowa 81.2%) |
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 (8)
Citizenship & Origin
Where residents were born and their citizenship status (Census ACS). 0.3% are foreign-born — below the U.S. average of 13.9%. 2% have naturalized to U.S. citizenship.
| Residents born in this state | 790 |
|---|---|
| Residents born in another state | 110 |
| Share born in this state | 86.2% |
| Share born in another state | 13.8% |
| Native-born U.S. citizens | 12.0% |
| Foreign-born residents | 0.3% |
| Naturalized citizens | 1.5% |
| Total foreign-born residents | 9 |
| From Europe | 4 |
Households & Family Composition
361 households. Averaging 2.5 people each — matches the U.S. average of 2.5. 78% are family households — above the U.S. share of ~65%. Of 285 families, 35% are married couples with children.
| Children under 18 | 245 |
|---|---|
| Total families | 285 |
| Married couples with children | 101 |
| Average household size | 2.54 |
| Women who gave birth (past year) | 5.5% |
| Grandparents living with grandchildren | 3 |
| Grandparents responsible for grandchildren | 3 |
| Family households | 280 households (vs Iowa 6,171) |
| Households that are families | 77.6% (vs Iowa 57.4%) |
| Total households | 361 households (vs Iowa 10,135) |
Sources: Census ACS 5-Year 2023 · Refreshed 2026-04-12
Residential Stability & Migration
How long residents have lived here and where they came from. 3.5% moved within the county in the past year — the U.S. baseline is roughly 8–10%. The surrounding county is losing 484 residents per year on net (IRS migration data).
| Moved within the county (past year) | 3.5% |
|---|---|
| Migration · People moving in (annual) | 112,688 |
| Migration · People moving out (annual) | 113,172 |
| Migration · Net migration (in − out) | -484 |
| 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 | 42 |
|---|---|
| Disability rate | 4.0% |
Other
| Congressional District · District | 1 |
|---|---|
| Congressional District · Congress | 118th |
| Cdc Birth Rate · Fips | 19013 |
| Cdc Birth Rate · State Fips | 19 |
| Cdc Birth Rate · County Fips | 013 |
| Cdc Birth Rate · County | Black Hawk |
| Cdc Birth Rate · Birth Rate | 14.7% |
| Cdc Birth Rate · Lower Ci | 13.00 |
| Cdc Birth Rate · Upper Ci | 16.50 |
| Cdc Mortality · Fips | 19013 |
| Cdc Mortality · County | Black Hawk County |
| Cdc Mortality · Urban Rural | Small metro |
| Cdc Mortality · Total Deaths 2020 2023 | 5,584 |
| Cdc Vaccination · Fips | 19013 |
| Cdc Vaccination · County | Black Hawk County |
| Cdc Vaccination · Dose1 Pop Pct | 68.1% |
| Cdc Vaccination · Series Complete Pct | 62.9% |
| Cdc Vaccination · Booster Pct | 57.7% |
| Cdc Vaccination · Population 2019 | 131,228 |
| Cdc Vaccination · Metro Status | Metro |
| Family Score · Score | 2.30 |
| Family Score · Schools | 2 |
| Family Score · Childcare Centers | 1 |
| Family Score · Children Pct | 21.2% |
| Family Score · Rating | limited |
| Town Summary · Key Facts | population 917, shrinking, established, affluent, mixed |
| Town Summary · Population | 917 people (vs Iowa 24,827) |
| Town Summary · County | Black Hawk County |
Sources: NCES school congressional district assignment · federal dataset cascade