Mercer County, New Jersey
County seat: Trenton · Population 399,289 (2025) · 225 sq mi
Mercer County is the 12th most populous of New Jersey's 21 counties, with 399,289 people (2025 estimate). Its county seat is Trenton, which is also the state capital. The map shows its 5 cities and towns and the 6 neighboring counties.
Mercer County facts
- County seat
- Trenton
- Population (2025 estimate)
- 399,289 +3.1% since 2020
- Land area
- 225 sq mi 16th largest of 21
- Water area
- 4 sq mi
- Population density
- 1,779 per sq mi
- Established
- 1838
- Same name
- One of 8 Mercer Counties in the US
- Named after
- Hugh Mercer Jacobite and General in the American Revolutionary War
- Largest city
- Hamilton 94,157
- Median household income
- $100,645
- Cities and towns
- 5 plus 13 CDPs
- ZIP codes
- 26
- Time zone
- Eastern
- FIPS code
- 34021
Cities and towns in Mercer County
Mercer County has 5 incorporated cities, towns and villages. Populations count the people living inside Mercer County; cities that cross a county line also list the other counties.
| Name | Type | Population 2025 | Also in |
|---|---|---|---|
| Trenton (county seat) | City | 91,506 | |
| Princeton | City | 31,469 | |
| Hightstown | Borough | 6,007 | |
| Pennington | Borough | 2,889 | |
| Hopewell | Borough | 1,944 |
Unincorporated communities (CDPs)
Census-designated places are communities without their own city government; the county provides their services.
| Community | Population | Also in |
|---|---|---|
| Mercerville | 13,535 | |
| Hamilton Square | 11,622 | |
| White Horse | 10,507 | |
| Twin Rivers | 8,382 | |
| Yardville | 6,301 | |
| Lawrenceville | 3,924 | |
| Robbinsville Center | 3,777 | |
| The College of New Jersey | 3,658 | |
| Groveville | 3,100 | |
| Princeton Junction | 2,025 | |
| Washington Crossing | 536 | |
| Titusville | 501 | |
| Windsor | 325 |
ZIP codes in Mercer County
26 ZIP codes reach into Mercer County. ZIP codes ignore county lines, so some also cover a neighboring county.
- 08501 also Monmouth and Burlington counties
- 08512 also Middlesex County
- 08520
- 08525 also Hunterdon and Somerset counties
- 08530 also Hunterdon County
- 08534
- 08540 also Somerset and Middlesex counties
- 08542
- 08544
- 08550
- 08558 also Somerset County
- 08560 also Hunterdon County
- 08561
- 08608
- 08609
- 08610 also Burlington County
- 08611
- 08618
- 08619
- 08620 also Burlington County
- 08628
- 08629
- 08638
- 08648
- 08690
- 08691 also Monmouth County
Population of Mercer County, 2020–2025
Mercer County grew by 11,955 people (+3.1%) between April 2020 and July 2025: 4,120 more births than deaths and a net gain of 8,143 people from migration.
| Year (July 1) | Population |
|---|---|
| 2020 | 386,434 |
| 2021 | 382,139 |
| 2022 | 387,024 |
| 2023 | 391,369 |
| 2024 | 397,329 |
| 2025 | 399,289 |
Neighboring counties
- Bucks County, Pennsylvania west · 647,828 people
- Middlesex County northeast · 883,335 people
- Hunterdon County northwest · 131,781 people
- Burlington County south · 481,439 people
- Monmouth County east · 651,035 people
- Somerset County north · 356,486 people
Printable Mercer County map
The PDF is a vector file with real text: it prints sharp on Letter paper and you can search it for a town. The PNG is 2400 pixels wide for slides and documents. Both are free to use with a credit to WhichCounty.
- PDF (Letter) (123 KB)
- PNG (2400 px) (102 KB)
Paste this code to embed the map on your site:
Sources
- Boundaries: U.S. Census Bureau, 2025 Cartographic Boundary Files (1:500,000).
- Population: Census Bureau county and city estimates, Vintage 2025. CDP populations: American Community Survey 2020–2024.
- Places and ZIP codes: Census Bureau 2026 Gazetteer and 2020 ZIP Code Tabulation Area relationship files.
- County seat, founding year and name origin: Wikidata (CC0), checked against state sources.
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