Trenton-New Brunswick Turnpike, the futureU.S. Route 1 through Mercer County, 1904Holder Tower inPrinceton University, one of the world's most prominentresearch universities[21]
The county was named forContinental ArmyGeneral Hugh Mercer, who died as a result of wounds received at theBattle of Princeton on January 3, 1777.[22] Continental Army Brigadier GeneralHugh Mercer served in the Continental Army during theBattle of Trenton and the Battle of Princeton in 1777. A Scotsman who had fled to British North America after the failedJacobite Rebellion, he worked closely with George Washington in the American Revolution. On January 3, 1777, Washington's army was en route to Princeton, New Jersey. While leading a vanguard of 350 soldiers, Mercer's brigade encountered two British regiments and a mounted unit. A fight broke out at an orchard grove and Mercer's horse was shot from under him. Getting to his feet, he was quickly surrounded by British troops who mistook him for George Washington and ordered him to surrender. Outnumbered, he drew his saber and began an unequal contest. He was finally beaten to the ground, bayoneted repeatedly (seven times), and left for dead. Legend has it that a beaten Mercer, with a bayonet still impaled in him, did not want to leave his men and the battle and was given a place to rest on a white oak tree's trunk, and those who remained with him stood their ground. TheMercer Oak, against which the dying general rested as his men continued to fight, appears on the county seal and stood for 250 years until it collapsed in 2000.[23]
Founded February 22, 1838, from portions of surrounding counties, Mercer County has a historical impact that reaches back to the pivotal battles of theAmerican Revolutionary War. On the night of December 25–26, 1776, GeneralGeorge Washington led American forcesacross the Delaware River to attack theHessian forces in theBattle of Trenton on the morning of December 26, also known as the First Battle of Trenton. After the battle, Washington crossed back to Pennsylvania. He crossed a third time in a surprise attack on the forces of GeneralCharles Cornwallis at theBattle of the Assunpink Creek, on January 2, 1777, also known as the Second Battle of Trenton, and at theBattle of Princeton on January 3. The successful attacks built morale among the pro-independence colonists.[24] Ewing Church Cemetery in Ewing is one of the oldest cemeteries in the area, having served the Ewing community for 300 years. It is home to the burial places of hundreds of veterans from The Revolutionary War to the Vietnam War.[25]
Since 1790,Trenton has served as the state's capital, earning the county the name "the Capital County." After the Legislature relocated to Trenton fromPerth Amboy in 1790, it purchased land for £250 and 5 shillings and constructed a new state house, designed by Philadelphia-based architect Jonathan Doane, beginning in 1792. The Doane building was covered in stucco, measured 150 by 50 feet (46 by 15 m), and housed the Senate and Assembly chambers in opposite wings. To meet the demands of the growing state, the structure was expanded several times during the 19th century. New Jersey, along with Nevada, is the only state to have its capital be located at the border with another state, as Trenton is across the Delaware River fromPennsylvania. Theofficial residence of thegovernor of New Jersey, known asDrumthwacket, is located inPrinceton, and is listed on both theU.S. National Register of Historic Places and theNew Jersey Register of Historic Places.
The county experienced rapid urbanization and population growth during the first half of the 20th century due to the growth of industrialization in places such as Trenton. Mercer County was the landing spot for a fictionalMartian invasion of the United States. In 1938, in what has become one of the most famous American radio plays of all time,Orson Welles acted out hisThe War of the Worlds invasion. His imaginary aliens first "landed" at what is nowWest Windsor. A commemorative monument is erected atGrovers Mill park.[26]
According to theU.S. Census Bureau, as of the 2020 Census, the county had a total area of 228.86 square miles (592.7 km2), of which 224.44 square miles (581.3 km2) was land (98.1%) and 4.42 square miles (11.4 km2) was water (1.9%).[3]
The county is generally flat and low-lying on the inner coastal plain, which extends up to theRoute 1 corridor. Further northwest, terrain rises as it ascends thePiedmont Plateau, withThe Sourlands encompassing the far northwestern portion of the county.Baldpate Mountain, in the western part ofHopewell Township, is the highest point in the county, at 480 feet (150 m) above sea level.[28] The lowest elevation is sea level, spread out along the shores of the tidal portions of theDelaware River,Crosswicks Creek and the smaller waterways within the Trenton-Hamilton Marsh inHamilton Township and the city ofTrenton.
According to theA. W. Kuchler U.S.potential natural vegetation types, most of Mercer County would have a dominant vegetation type of AppalachianOak (104) with a dominant vegetation form of EasternHardwood Forest (25) with a dominant section of Northeastern Oak/Pine (110) Southern Mixed Forest (26) in the far east near Hightstown.[34]
Mercer County, New Jersey – Racial and ethnic composition Note: the US Census treats Hispanic/Latino as an ethnic category. This table excludes Latinos from the racial categories and assigns them to a separate category. Hispanics/Latinos may be of any race.
As of the2020 United States census, Mercer County has a population of 387,340, making it the 12th most populous county in the state. The racial makeup of the county is quite diverse with 62.3% of the population identifying as white (and 46.7% as non-Hispanic whites), 21.6% of the population being black/African American, and 12.6% of the county's population identifying as Asian. 19.4% of Mercer County is Hispanic/Latino, 0.9% of the population is American Native/Alaskan Native/Native Hawaiian/Pacific Islander, and 2.6% identify as two or more races.[4]
5.4% of Mercer County is under the age of 5, while 21.2% are under the age of 18, and 16.0% are over the age of 65. The female population of the county stands at 50.8%, which is in line with the state as a whole.[4]
There are 150,657 housing units in Mercer County, with 63.5% of them being owned by the occupiers. There are 131,440 households with an average of 2.67 persons per household.[4]
The2010 United States census counted 366,513 people, 133,155 households, and 89,480 families in the county. Thepopulation density was 1,632.2 per square mile (630.2/km2). There were 143,169 housing units at an average density of 637.6 per square mile (246.2/km2). The racial makeup was 61.39% (225,011)White, 20.28% (74,318)Black or African American, 0.33% (1,194)Native American, 8.94% (32,752)Asian, 0.08% (295)Pacific Islander, 6.24% (22,856) fromother races, and 2.75% (10,087) from two or more races.Hispanic or Latino of any race were 15.09% (55,318) of the population.[16]
Of the 133,155 households, 31.4% had children under the age of 18; 48.2% were married couples living together; 14.2% had a female householder with no husband present and 32.8% were non-families. Of all households, 26.9% were made up of individuals and 10.1% had someone living alone who was 65 years of age or older. The average household size was 2.61 and the average family size was 3.16.[16]
22.6% of the population were under the age of 18, 10.9% from 18 to 24, 26.9% from 25 to 44, 26.9% from 45 to 64, and 12.6% who were 65 years of age or older. The median age was 37.8 years. For every 100 females, the population had 95.5 males. For every 100 females ages 18 and older there were 93 males.[16]
In 2015, the county had aper capita personal income of $63,720, the sixth-highest in New Jersey, and ranked 121st of 3,113 counties in the United States.[46][47] Mercer County stands among thehighest-income counties in the United States, with theBureau of Economic Analysis having ranked the county as having the 78th-highestper capita income of all 3,113 counties in the United States (and the sixth-highest in New Jersey) as of 2009.[48] Trenton's role as New Jersey's state capital contributes significantly to Mercer County's economic standing. 9.5% of the population is considered at or below the poverty line.
The median household income in Mercer County is $83,306. 89.6% of the population has a high school diploma, and 43.5% of the county's population has a bachelor's degree or higher, one of the highest rates in the state, as of the 2020 census.[4]
Mercer County has acounty executive form of government, in which the Mercer County Executive performs executive functions, administering the operation of the county, and a Board of County Commissioners acts in a legislative capacity.[49][50][51] The county executive is directly elected to a four-year term of office. The seven-memberBoard of County Commissioners, previously known as the Board of Chosen Freeholders, is elected at-large to serve three-year staggered terms of office on a staggered basis, with either two or three seats up for election each year. The Board is led by a Commissioner Chair and vice-chair, selected from among its members at an annual reorganization meeting held in January. The Commissioner Board establishes policy and provides a check on the powers of the County Executive. The Board approves all county contracts and gives advice and consent to the County Executive's appointments of department heads, and appointments to boards and commissions. The Commissioner Board votes to approve the budget prepared by the Executive after review and modifications are made.[52] In 2016, freeholders were paid $29,763 and the freeholder director was paid an annual salary of $31,763.[53] That year, the county executive was paid $164,090 per year.[54]
Pursuant to Article VII Section II of theNew Jersey State Constitution, each county in New Jersey is required to have three elected administrative officials known as "constitutional officers." These officers are theCounty Clerk andCounty Surrogate (both elected for five-year terms of office) and theCounty Sheriff (elected for a three-year term).[65] Mercer County's constitutional officers are:
Title
Representative
County Clerk
Paula Sollami-Covello (D, Lawrence Township, 2025),[66][67]
Sheriff
John A. Kemler (D, Hamilton Township, 2026)[68][69]
Surrogate
Diane Gerofsky (D, Lawrence Township, 2026).[70][71][72]
No Republican has won countywide office since 2000. Law enforcement on the county level is provided by the Mercer County Sheriff's Office and the Mercer County Prosecutor's Office. The Mercer County Prosecutor is Angelo J. Onofri of Hamilton Township, who took office in December 2016 after being nominated byGovernor of New JerseyChris Christie and being confirmed by theNew Jersey Senate.[73][74] Mercer County constitutes Vicinage 7 of theSuperior Court of New Jersey.[75] The vicinage is seated at the Mercer County Criminal Courthouse, located at 400 South Warren Street inTrenton.[75] The vicinage has additional facilities for the Civil, Special Civil, General Equity, and Family Parts at the Mercer County Civil Courthouse, located at 175 South Broad Street, also in Trenton.[75] The Assignment Judge for Mercer County is Mary C. Jacobson.[75]
Mercer County is a reliably Democratic county; it has gone for Republicans only three times (in1956,1972,1984) since1936. In each presidential election of the 21st century, the Democratic candidate earned at least 60% of the vote. Since the 2008 election, every municipality has voted for the Democratic candidate, and in the 2024 election, it was the 2nd most Democratic county in the state. This comes afterJoe Biden won the county by 40.0% in2020, the widest margin for anyone since1964. As of October 1, 2021, there were a total of 265,703 registered voters in Mercer County, of whom 121,653 (45.8%) were registered asDemocrats, 41,701 (15.7%) were registered asRepublicans and 98,343 (37.0%) were registered asunaffiliated. There were 4,006 voters (1.5%) registered to other parties.[82]
United States Senate election results for Mercer County, New Jersey1[83]
Mercer County has county routes, state routes, U.S. Routes and Interstates that all pass through. As of 2010[update], the county had a total of 1,524.30 miles (2,453.12 km) of roadways, of which 1,216.48 miles (1,957.73 km) were maintained by the local municipality, 175.80 miles (282.92 km) by Mercer County, 118.99 miles (191.50 km) by theNew Jersey Department of Transportation, 1.19 miles (1.92 km) by theDelaware River Joint Toll Bridge Commission and 12.43 miles (20.00 km) by theNew Jersey Turnpike Authority.[86]
Mercer County is served by the following major roadways:[87]
I-295 functions as a partial ring-road around the Trenton area, while I-195 serves as an east–west expressway from Trenton to theJersey Shore. The New Jersey Turnpike (I-95) passes through the southeastern section of the county, and serves as a major corridor toDelaware,Washington, D.C. to the south, andNew York City andNew England towards the north. Two turnpike interchanges are located within Mercer County: Exit 7A inRobbinsville Township and Exit 8 inEast Windsor Township.
Before 2018, Interstate 95 abruptly ended at the interchange with US 1 inLawrence Township, and became I-295 south. Signs directed motorists to the continuation of I-95 by using I-295 to I-195 east to the New Jersey Turnpike. This was all due in part to the cancellation of theSomerset Freeway that was supposed to go fromHopewell Township in Mercer County up toFranklin Township inSomerset County.[88]
The section of I-95 west of the US 1 interchange in Lawrence was re-numbered as part of I-295 in March 2018, six months before adirect interchange withInterstate 95 in Pennsylvania and thePennsylvania Turnpike opened.[89] This planned interchange indirectly prompted another project: the New Jersey Turnpike Authority extended the 'dual-dual' configuration (inner car lanes and outer truck / bus / car lanes) to Interchange 6 inMansfield Township,Burlington County from its former end at Interchange 8A inMonroe Township,Middlesex County. This widening was completed in early November 2014.[90]
NJ Transit'sRiver Line connects Trenton toCamden, with three stations in the county, all within Trenton city limits, atCass Street,Hamilton Avenue and at the Trenton Transit Center.[92]
^Princeton Township andPrinceton Borough merged on January 1, 2013. The data is tabulated from the sum of the two municipalities' 2010 populations and areas. Though it has a borough form of government, the municipality type is classified by the state government as "other."[96]
^Governor Murphy Settles Central Jersey Debate,Governor of New JerseyPhil Murphy, press release dated August 4, 2023. "Governor Phil Murphy today signed S3206 to promote Central Jersey tourism.... The 'Central Jersey' region will be comprised of, at minimum, the counties of Hunterdon, Mercer, Middlesex, and Somerset."
^Willis, David P."'This is how wars start': Does Central Jersey include both Ocean and Union counties?",Asbury Park Press, February 20, 2023. Accessed March 31, 2024. "North Jersey is defined as Sussex, Warren, Morris, Passaic, Bergen, Essex and Hudson counties; South Jersey would be Burlington, Camden, Gloucester, Atlantic, Salem, Cumberland and Cape May counties. But for Central, things get a little tricky. It would include Hunterdon, Somerset, Union, Middlesex, Mercer, Monmouth, and Ocean counties."
^Princeton Battlefield's Mercer OakArchived January 21, 2014, at theWayback Machine, Princeton Battlefield's Clarke House Volunteers. Accessed October 6, 2013. "This white oak later became the symbol for Mercer County (named for the general), Princeton Township, the NJ Green Acres program, and other agencies. The approximately 250-year-old tree collapsed of its own weight March 3, 2000."
^Staff."Hughes, Officials unveil section of steel beam from Sept. 11 to be used in memorial"Archived October 16, 2012, at theWayback Machine, Mercer County press release dated March 28, 2011. Accessed September 11, 2011. "Mercer County Executive Brian M. Hughes was flanked by firefighters and first responders from around the County today as a section of a steel beam recovered from Ground Zero was displayed for the first time. The 10-foot, 2,108-pound piece of I-beam steel was recovered from Ground Zero during the aftermath of the September 11, 2001 attacks.... Dozens of firefighters and first responders from Mercer County worked at Ground Zero for the first 10 days after September 11, Hughes said. Mercer County was also home to 27 victims."
^The Prosecutor - Angelo J. Onofri, ProsecutorArchived October 26, 2017, at theWayback Machine, Mercer County's Prosecutor Office. Accessed October 25, 2017. "Angelo J. Onofri was sworn in as Mercer County prosecutor on December 28, 2016, after being appointed by Governor Chris Christie and unanimously confirmed by the New Jersey Senate. He had been serving as acting prosecutor since March 1, 2015."
^Biography, Congresswoman Bonnie Watson Coleman. Accessed January 3, 2019. "Watson Coleman and her husband William reside in Ewing Township and are blessed to have three sons; William, Troy, and Jared and three grandchildren; William, Kamryn and Ashanee."
^Frassinelli, Mike."N.J., Pennsylvania officials plan to close longtime gap on Route 95"Archived September 10, 2010, at theWayback Machine,The Star-Ledger, September 7, 2010. Accessed October 24, 2017. "Plans to run I-95 north of Trenton to Route 287 near Perth Amboy as part of the 'Somerset Freeway' were scuttled in 1980 after residents in the Princeton area feared a potential loss in property values and their small-town feel."
^Nadeau, Gregory G. (May 20, 2015)."FHWA to AASHTO I-95 Designation"(PDF). Letter to Bud Wright. Washington, DC: Federal Highway Administration. Archived fromthe original(PDF) on June 9, 2015. RetrievedJune 8, 2015.
^Zedalis, Joe."Trenton Titans fans still waiting for ticket refunds for canceled season"Archived February 20, 2015, at theWayback Machine,Times of Trenton, May 7, 2013. Accessed January 11, 2015. "The struggling Trenton Titans ice hockey franchise has yet to return advance ticket money to fans who purchased seats for the now-canceled 2013-2014 season, leaving some people waiting for refunds of up to $2,000. The team announced April 23 that they would not be returning to the ice in October."
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