Mercer County vs Monmouth County
Two neighbouring counties in New Jersey, compared on population, size, income and housing. They share 14 mi of border.
Mercer County
New Jersey
Monmouth County
New Jersey
Both outlines are drawn at true relative size. Monmouth County spans about 53.9 km at its widest.
Side by side
| Measure | Mercer County | Difference | Monmouth County |
|---|---|---|---|
| Population | 399,289 | -38.7% | 651,035 |
| Change since 2020 | 3.3% | +2.0 pp | 1.3% |
| Land area | 224.5 sq mi | -52.1% | 468.2 sq mi |
| Population density | 1,779 per sq mi | +28.0% | 1,390 per sq mi |
| Median household income | $100,645 | -19.4% | $124,845 |
| Median home value | $377,700 | -37.7% | $606,100 |
| Median age | 39.5 | -8.6% | 43.2 |
| Households | 144,114 | -42.7% | 251,712 |
| Housing units | 151,138 | -44.1% | 270,415 |
Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; US Census Bureau, American Community Survey, American Community Survey 2020-2024 5-Year Estimates, released 29 January 2026; US Census Bureau, County Adjacency File, 2025 County Adjacency File, released 15 September 2025. The difference column is computed here: the first county's figure against the second, expressed as a percentage of the second. The change-since-2020 row is the exception: two growth rates differ in percentage points (pp), not percent. Retrieved 30 August 2026.
What the numbers say
- Monmouth County holds about 1.6 times the population of Mercer County: 651,035 against 399,289.
- Monmouth County covers more ground, at 468.2 square miles against 224.5.
- Mercer County is the more crowded of the two, at 1,779 people per square mile against 1,390.
- Median household income is higher in Monmouth County, by 24,200 dollars a year.
- Since 2020, Mercer County has grown by 3.3% and Monmouth County has grown by 1.3%.
- They share 14 mi of common border, which the Census Bureau publishes in its county adjacency file and which almost no other county reference presents.
Full pages
Want a different pair? Compare any two of the 3,144 US counties.
Rebuilt from source data 30 August 2026. How these figures are produced.