Mercer County, New Jersey population
County or county equivalent · Official geographic code 34021
· Annual resident population estimate
U.S. Census Bureau · Population Estimates Program · Vintage 2025
+1,960 residents (+0.49%) since July 1, 2024.
- Population change, 2020–2025
- +12,855July 1 to July 1 · +3.33%
- Land-area density, 2025
- 1,778.7People per square mile · 2025 land area
- Population rank, 2025
- 196 of 3,144U.S. counties and county equivalents
Mercer County population history
Open historical explorerThese six July 1 estimates belong to one consistent Vintage 2025 series. The Census Bureau revises earlier years when it releases a new vintage; a figure from an older publication may differ from the value below.
Annual estimates · 2020–2025 · Vertical scale shown on chart.
The highest observed population in this annual series was 399,289 in 2025. This is a peak within 2020–2025 coverage, not an all-time record.
| Reference date | Population | Annual change |
|---|---|---|
| July 1, 2020 | 386,434 | — |
| July 1, 2021 | 382,139 | -4,295 |
| July 1, 2022 | 387,024 | +4,885 |
| July 1, 2023 | 391,369 | +4,345 |
| July 1, 2024 | 397,329 | +5,960 |
| July 1, 2025 | 399,289 | +1,960 |
Why is the April 2020 estimates base different from a census count?
The PEP estimates base here is 387,334 residents on April 1, 2020. It incorporates the Census Bureau’s corrections and geographic revisions and serves as the starting point for this annual series. It is not labeled an original 2020 census count. The chart starts at July 1, 2020, so its five-year change uses two July observations. Read about measurement types.
Growth and density
Between July 1, 2020 and July 1, 2025, Mercer County gained 12,855 residents, a 3.33% increase. The annualized change over these five elapsed years was +0.66%. Annualized change is a summary of the interval; it does not imply that the population changed at that rate in every year.
The 2025 Gazetteer reports 224.48 square miles of land. Dividing the July 1, 2025 population by that compatible land area gives 1,778.7 people per square mile. Water area is excluded. Density depends on geographic boundaries. It describes this entire geography, rather than a typical neighborhood or built-up area.
Calculations use unrounded source values. Population counts are displayed as integers, percentages to two decimals and density to one decimal. Calculation methods · Growth calculator
Components of population change
The published components cover July 1, 2024 through June 30, 2025. Natural change equals births minus deaths. Net migration is arrivals minus departures; it does not establish why people moved.
| Component | People |
|---|---|
| Births | 4,178 |
| Deaths | 3,096 |
| Natural change | +1,082 |
| Net domestic migration | -2,240 |
| Net international migration | +3,089 |
| Residual | +29 |
| Total population change | +1,960 |
Reconciliation: natural change + net domestic migration + net international migration + residual = +1,960. Births and deaths are already included in natural change and must not be added again. Source: co-est2025-alldata.csv; Vintage 2025.
Age structure, race and Hispanic-origin panels are not included in this totals release. Their separate periods, definitions and uncertainty will be validated before publication. Coverage details.
Geographic context
County equivalents include parishes, boroughs, census areas, independent cities, DC and Connecticut planning regions where represented by Census. The places listed below are whole-city observations and can extend into other counties. Summing them will not reproduce this county total.
| Place | Population · 2025 | Change · 2024–25 | Growth · 2024–25 | People / sq. mi. |
|---|---|---|---|---|
| TrentonNew Jersey · Incorporated place · 3474000 | 91,506 | +196 | +0.21% | 12,030.3 |
| PrincetonNew Jersey · Incorporated place · 3460900 | 31,469 | +23 | +0.07% | 1,753.6 |
| HightstownNew Jersey · Incorporated place · 3431620 | 6,007 | +19 | +0.32% | 4,870.6 |
| PenningtonNew Jersey · Incorporated place · 3457600 | 2,889 | +8 | +0.28% | 3,006.5 |
| HopewellNew Jersey · Incorporated place · 3433150 | 1,944 | +3 | +0.15% | 2,686.3 |
Showing 5 of 5 related records.
New Jersey population · State city directory · City proper versus county versus metro
Places with nearby population ranks
Selected from the same 2025 comparison universe, using neighboring population ranks. Similar population does not imply similar density, boundaries or demographics.
| Place | Population · 2025 | Change · 2024–25 | Growth · 2024–25 | People / sq. mi. |
|---|---|---|---|---|
| Butler CountyOhio · County equivalent · 39017 | 400,128 | +2,347 | +0.59% | 857.7 |
| Douglas CountyColorado · County equivalent · 08035 | 399,396 | +6,345 | +1.61% | 475.0 |
| Chesterfield CountyVirginia · County equivalent · 51041 | 397,148 | +5,905 | +1.51% | 937.8 |
| Hamilton CountyTennessee · County equivalent · 47065 | 390,833 | +3,565 | +0.92% | 720.9 |
Source, citation and downloads
U.S. Census Bureau, Population Estimates Program, Vintage 2025, co-est2025-alldata.csv, variable POPESTIMATE2025; Mercer County, New Jersey, geographic code 34021; resident population 399,289 on July 1, 2025; boundaries January 1, 2025. https://www2.census.gov/programs-surveys/popest/datasets/2020-2025/counties/totals/co-est2025-alldata.csv. Retrieved September 30, 2026. US Population Data snapshot pep-2025-r1, transformation 1.
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