392,138 people (2024 Census estimate, +1.5% since 2020)
224 square miles of land · 1,747 people per square mile
“Highest” and “lowest” are just order, not grades: a high rank for poverty or hazard losses means more of it. Each figure's source is in its section below.
11 active community water systems list Mercer County in the area they serve, reporting 302,534 people served in all (a system that crosses county lines counts its whole population).
| TRENTON WATER WORKS surface water · local government · NJ1111001 | 217,000 served |
| AQUA NJ - HAMILTON SQUARE buys surface water · private · NJ1103001 | 39,128 served |
| EAST WINDSOR MUA groundwater · local government · NJ1101002 | 25,000 served |
| AQUA NJ - LAWRENCE groundwater (surface-influenced) · private · NJ1107002 | 8,655 served |
| HIGHTSTOWN WATER DEPARTMENT groundwater · local government · NJ1104001 | 5,400 served |
| PENNINGTON W DEPT groundwater · local government · NJ1108001 | 2,600 served |
| HOPEWELL BORO W DEPT buys surface water · local government · NJ1105001 | 2,035 served |
| LAWRENCEVILLE SCHOOL groundwater · private · NJ1107001 | 1,200 served |
Source: U.S. EPA Safe Drinking Water Information System (SDWIS), active community systems, . Look up any system's violations and test results with EPA's search using its ID.
About 443 people were held in Mercer County's jail, in Vera's latest figure (2023), or 177 per 100,000 residents ages 15–64. In 2018 it was about 478.
Source: Vera Institute of Justice, Incarceration Trends (built from federal Bureau of Justice Statistics jail surveys). Counties without their own jail, or that share one, may show no figure.
11 school districts have their office in Mercer County. School taxes are usually the largest part of a property tax bill.
Spent $466.5 million — $400.7 million to run schools, about $26,980 per student, plus $7.5 million on buildings and equipment. Money in: $27.8 million local (mostly property tax), $402.6 million state, $49.3 million federal. Long-term debt: $9.6 million.
Spent $292.5 million — $278.2 million to run schools, about $22,996 per student, plus $6.5 million on buildings and equipment. Money in: $132.1 million local (mostly property tax), $147.8 million state, $21.3 million federal. Long-term debt: $61.6 million.
Spent $251.4 million — $222 million to run schools, about $24,595 per student, plus $20 million on buildings and equipment. Money in: $185.1 million local (mostly property tax), $58.7 million state, $5.8 million federal. Long-term debt: $127 million.
Spent $142.9 million — $125.9 million to run schools, about $24,497 per student, plus $11.2 million on buildings and equipment. Money in: $75.6 million local (mostly property tax), $65.4 million state, $7 million federal. Long-term debt: $15.8 million.
Spent $130.7 million — $120.6 million to run schools, about $31,587 per student, plus $5.2 million on buildings and equipment. Money in: $96.1 million local (mostly property tax), $30.4 million state, $3 million federal. Long-term debt: $44 million.
Spent $108.5 million — $100 million to run schools, about $26,939 per student, plus $4.1 million on buildings and equipment. Money in: $79.1 million local (mostly property tax), $26.7 million state, $4.2 million federal. Long-term debt: $30.2 million.
Spent $115.9 million — $99.4 million to run schools, about $28,031 per student, plus $9.3 million on buildings and equipment. Money in: $65.8 million local (mostly property tax), $37.6 million state, $7.1 million federal. Long-term debt: $55 million.
Spent $115.8 million — $111.1 million to run schools, about $31,986 per student, plus $2.6 million on buildings and equipment. Money in: $87.1 million local (mostly property tax), $26.5 million state, $2.6 million federal. Long-term debt: $33.9 million.
And 3 more.
Source: U.S. Census Bureau, 2023 Annual Survey of School System Finances. Districts are listed by the county of their main office; some serve neighboring counties too.
Source: County Health Rankings & Roadmaps 2025 (University of Wisconsin Population Health Institute), which gathers federal data (CDC, Census, and others); measures cover different recent years. Blank lines aren't reported for small counties.
Overall risk: Relatively High compared with other U.S. counties. FEMA estimates natural hazards cost Mercer County about $176.2 million a year on average in buildings, crops and lives. Ability to bounce back (community resilience): Relatively High; social vulnerability: Relatively Moderate.
Source: FEMA National Risk Index (December 2025), expected annual loss. Ratings compare counties nationwide; they're estimates, not predictions.
413 bridges in Mercer County: 165 in good condition, 212 fair, and 36 poor (8.7%). “Poor” means a main part — the deck, the beams, or the supports — is rated 4 or lower on the federal 0–9 scale. It doesn't mean unsafe to drive; unsafe bridges are closed.
| US ROUTE 1 over D&R CANAL · built 1973 | 43,117 vehicles a day |
| QUAKER BRIDGE ROAD over AMTRAK · built 1966 | 33,105 vehicles a day |
| US 130 over MILLSTONE RIVER · built 1936 | 32,880 vehicles a day |
| SOUTH OLDEN AVENUE over AMTRAK NE CORRIDOR · built 1923 | 22,960 vehicles a day |
| U.S. 1B over FIVE MILE RUN · built 1928 | 22,136 vehicles a day |
| QUKRBRDG RD CR533 over MIRY RUN · built 1936 | 20,985 vehicles a day |
Source: Federal Highway Administration, National Bridge Inventory (2025 submission). Includes state, county and city bridges.
Federal grants paid for $2.5 billion of work in Mercer County in fiscal 2025, about $6,374 per resident — to the county, cities, schools, hospitals, nonprofits and others.
Source: USAspending.gov, grants by place of performance, fiscal 2025 (Oct. 2024 to Sept. 2025). Search it by county to see each award.
From Grants.gov: posted grants listing county governments as eligible, soonest deadline first; research-only and overseas programs left out; list updated 2026-10-13, refreshed weekly. 62 are open in all. Cities, towns, school districts and nonprofits have their own lists there.
Registration deadlines, early voting and polling places for New Jersey are on the federal site vote.gov, which links to the state's official election office.
The budget, property tax rates, audits, local officials and offices for Mercer County come from the county's own records, which we haven't gathered — not gathered, never hidden. See what a full county site looks like, or ask to have Mercer County built: brayden.ozark@gmail.com.
More of New Jersey: the state government and every county in New Jersey.
Nearby counties: Middlesex County (19 mi) · Somerset County (20 mi) · Bucks County, PA (22 mi) · Hunterdon County (22 mi) · Burlington County (28 mi) · Monmouth County (29 mi).