Seneca: Demographics & People
Census counts 2,450 people in Seneca, in 907 households. Population shrank 3.0% from 2,525 (2022) to 2,450 (2024). Median age 35.5 years. (6.7y younger than LaSalle County; 2.2y younger than Illinois). Children under 18 are 29% of the population. Population is 87% White (non-Hispanic) and 10% Hispanic or Latino. The community is relatively homogeneous (Simpson index 0.14). 71% of households are family-led. County health: 35% adult obesity, 13% smoke.
- 2.7 people per household (vs Illinois avg 2.5).
- 29% non-family households (singles, roommates) (vs Illinois 38%).
- 69 dependents per 100 working-age (youth + seniors / 18-64) (vs Illinois 64).
Population & Trend
Population shrank 3.0% from 2,525 (2022) to 2,450 (2024). Estimated 2026 population: ~2,377 (extrapolated at -1.5%/yr trend). Census Bureau Vintage estimate: 2,283.
| Census data vintage | 2024 |
|---|---|
| Population | 52,533 people |
| Annual growth rate · Population change | -3.0% |
| Annual growth rate · Population (2022) | 2,525 |
| Annual growth rate · Population (2024) | 2,450 |
| Annual growth rate · Trend category | declining |
| Population | 2,450 people (vs Illinois 39,460) |
| Population Estimate | 2,283 |
Sources: Census ACS 5-Year 2023, Table B01003 · Refreshed 2026-04-12
Age Distribution
Median age 35.5y is 3.4 years younger than the U.S. median (38.9y). Children under 18 make up 29% — above the U.S. share of ~22%.
| Age Summary · Median age | 35.5 years (vs Illinois 37.7y) |
|---|---|
| Age Summary · Children Pct | 28.6% |
| Age Summary · Character | family-oriented |
| Age Summary · Total Pop | 2,450 |
| Age Summary · Under 18 | 701 |
| Age Summary · 18 To 34 | 500.0× |
| Age Summary · 35 To 64 | 953.0× |
| Age Summary · 65 Plus | 296 |
| Population under 18 | 701 |
| Median age | 35.5 years (vs Illinois 37.7y) |
Sources: Census ACS 5-Year 2024 — place-level B01001 query · Census ACS 5-Year 2023 · Refreshed 2026-04-29
Race, Ethnicity & Diversity
Of 2,450 residents, race / ethnicity breaks down by Census ACS counts (a person can identify with one or more groups). The Simpson diversity index is 0.14 (0 = single group, 1 = perfectly even distribution); this is read as relatively homogeneous.
| White residents | 2,269 |
|---|---|
| Black residents | 28 |
| Hispanic or Latino residents | 151 |
| Diversity Index · Diversity index (Simpson) | 13.7% |
| Diversity Index · Diversity label | relatively homogeneous |
| Diversity Index · Groups counted | 3 |
| Diversity Index · Largest group share | 92.7% |
| Black population | 0.9% (vs Illinois 9.3%) |
| Hispanic or Latino population | 10.0% (vs Illinois 17.6%) |
| White (non-Hispanic) population | 86.6% (vs Illinois 54.8%) |
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). 0.4% are foreign-born — below the U.S. average of 13.9%. 2% have naturalized to U.S. citizenship.
| Residents born in this state | 1,936 |
|---|---|
| Residents born in another state | 453 |
| Share born in this state | 79.0% |
| Share born in another state | 21.0% |
| Native-born U.S. citizens | 18.5% |
| Foreign-born residents | 0.4% |
| Naturalized citizens | 2.0% |
| Total foreign-born residents | 41 |
Households & Family Composition
907 households. Averaging 2.7 people each — larger than the U.S. average of 2.5. 71% are family households — above the U.S. share of ~65%. Of 684 families, 20% are married couples with children.
| Children under 18 | 701 |
|---|---|
| Total families | 684 |
| Married couples with children | 136 |
| Single-parent households | 53 |
| Average household size | 2.72 |
| Women who gave birth (past year) | 15.6% |
| Grandparents living with grandchildren | 22 |
| Grandparents responsible for grandchildren | 16 |
| Family households | 643 households (vs Illinois 9,709) |
| Households that are families | 70.9% (vs Illinois 62.4%) |
| Total households | 907 households (vs Illinois 14,867) |
Sources: Census ACS 5-Year 2023 · Refreshed 2026-04-12
Residential Stability & Migration
How long residents have lived here and where they came from. 3.0% moved within the county in the past year — the U.S. baseline is roughly 8–10%.
| Moved within the county (past year) | 3.0% |
|---|---|
| Migration · People moving in (annual) | 53,347 |
| Migration · People moving out (annual) | 53,341 |
| Migration · Net migration (in − out) | 6 |
| 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 | 129 |
|---|---|
| Disability rate | 5.0% |
Other
| Congressional District · District | 16 |
|---|---|
| Congressional District · Congress | 118th |
| Cdc Birth Rate · Fips | 17063 |
| Cdc Birth Rate · State Fips | 17 |
| Cdc Birth Rate · County Fips | 063 |
| Cdc Birth Rate · County | Grundy |
| Cdc Birth Rate · Birth Rate | 11.3% |
| Cdc Birth Rate · Lower Ci | 9.10 |
| Cdc Birth Rate · Upper Ci | 13.80 |
| Cdc Mortality · Fips | 17063 |
| Cdc Mortality · County | Grundy County |
| Cdc Mortality · Urban Rural | Large fringe metro |
| Cdc Mortality · Total Deaths 2020 2023 | 1,541 |
| Cdc Vaccination · Fips | 17063 |
| Cdc Vaccination · County | Grundy County |
| Cdc Vaccination · Dose1 Pop Pct | 64.2% |
| Cdc Vaccination · Series Complete Pct | 59.4% |
| Cdc Vaccination · Booster Pct | 52.8% |
| Cdc Vaccination · Population 2019 | 51,054 |
| Cdc Vaccination · Metro Status | Metro |
| Family Score · Score | 3.10 |
| Family Score · Schools | 3 |
| Family Score · Childcare Centers | 2 |
| Family Score · Children Pct | 28.6% |
| Family Score · Rating | fair |
| Town Summary · Key Facts | population 2,450, declining, family-oriented, upper-middle, mixed |
| Town Summary · Population | 2,450 people (vs Illinois 39,460) |
| Town Summary · County | Grundy County |
Sources: NCES school congressional district assignment · federal dataset cascade