Mercer County is a county located in the U.S. state of New Jersey. Its county seat is Trenton, also the state capital,New Jersey County Map, New Jersey Department of State. Accessed December 22, 2022. prompting its nickname The Capital County. Mercer County alone constitutes the Trenton–Princeton metropolitan statistical areaRevised Delineations of Metropolitan Statistical Areas, Micropolitan Statistical Areas, and Combined Statistical Areas, and Guidance on Uses of the Delineations of These Areas and is considered part of the New York combined statistical area by the U.S. Census Bureau,(Note: Mercer County, NJ is NOT part of the Philadelphia CSA according to this original source.) "Revised Delineations of Metropolitan Statistical Areas, Micropolitan Statistical Areas, and Combined Statistical Areas, and Guidance on Uses of the Delineations of These Areas", OMB Bulletin no. 18-04, The White House, Office of Management and Budget, September 4, 2018NEW JERSEY - Core Based Statistical Areas (CBSAs) and Counties , United States Census Bureau, February 2013. Accessed August 8, 2017.Combined Statistical Areas of the United States and Puerto Rico , United States Census Bureau, July 2015. Accessed August 8, 2017. but also directly borders the Philadelphia metropolitan area and is included within the Federal Communications Commission's Philadelphia Designated Media Market Area.- Philadelphia Market Area Coverage Maps , Federal Communications Commission. Accessed December 28, 2014. The county is part of the Central Jersey region of the state.Governor Murphy Settles Central Jersey Debate, Governor of New Jersey Phil 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.""Regions: North, Central, South, Shore - Best of NJ", Best of NJ, Accessed May 30, 2024. "Central Jersey consists of Hunterdon, Mercer, Middlesex, Somerset, and Union County."
As of the 2020 United States census, the county retained its position as the state's 12th-most-populous county,Table 1. New Jersey Counties and Most Populous Cities and Townships: 2020 and 2010 Censuses, New Jersey Department of Labor and Workforce Development. Accessed December 1, 2022. with a population of 387,340, its highest decennial count ever and an increase of 20,827 (+5.7%) from the 366,513 recorded at the 2010 census, which in turn had reflected an increase of 15,752 (+4.5%) from the 350,761 enumerated at the 2000 census, United States Census Bureau. Accessed January 21, 2013.NJ Labor Market Views , New Jersey Department of Labor and Workforce Development, March 15, 2011. Accessed October 6, 2013. The United States Census Bureau's Population Estimates Program estimated a 2025 population of 399,289, an increase of 11,949 (+3.1%) from the 2020 decennial census. The most populous municipality in Mercer County at the 2020 census was Hamilton Township, with 92,297 residents, while Hopewell Township was the largest in area.
The county was formed by an act of the New Jersey Legislature on February 22, 1838, from portions of Burlington County (Nottingham Township, now Hamilton Township), Hunterdon County (Ewing Township, Lawrence Township, Trenton, and portions of Hopewell Township), and Middlesex County (West Windsor and portions of East Windsor).Snyder, John P. The Story of New Jersey's Civil Boundaries: 1606-1968 , Bureau of Geology and Topography; Trenton, New Jersey; 1969. p. 161. Accessed October 1, 2013. The former Keith Line bisects the county and is the boundary between municipalities that previously had been separated into West Jersey and East Jersey.
Trenton–Mercer Airport in Ewing Township is a commercial and corporate aviation airport serving Mercer County and its surrounding vicinity. Princeton is home to Princeton University, an Ivy League research university, and to Drumthwacket, the official residence of the governor of New Jersey. Mercer County contains 12 municipalities, the fewest of any county in New Jersey, and equal to Hudson County.
Etymology The county was named for Continental Army General Hugh Mercer, who died as a result of wounds received at the Battle of Princeton on January 3, 1777.Kane, Joseph Nathan; and Aiken, Charles Curry. The American Counties: Origins of County Names, Dates of Creation, and Population Data, 1950-2000, p. 201. Scarecrow Press, 2005. . Accessed January 21, 2013. Continental Army Brigadier General Hugh Mercer served in the Continental Army during the Battle of Trenton and the Battle of Princeton in 1777. A Scotsman who had fled to British North America after the failed Jacobite 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. The Mercer 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.Princeton Battlefield's Mercer Oak , 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."
History Founded February 22, 1838, from portions of surrounding counties, Mercer County has a historical impact that reaches back to the pivotal battles of the American Revolutionary War. On the night of December 25–26, 1776, General George Washington led American forces across the Delaware River to attack the Hessian forces in the Battle 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 General Charles Cornwallis at the Battle of the Assunpink Creek, on January 2, 1777, also known as the Second Battle of Trenton, and at the Battle of Princeton on January 3. The successful attacks built morale among the pro-independence colonists.Epicenter of Revolution , Mercer County. Accessed October 6, 2013. 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.Ewing Church Cemetery & Mausoleum
Since 1790, Trenton has served as the state's capital, earning the county the name "the Capital County." After the Legislature relocated to Trenton from Perth 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 , 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 from Pennsylvania. The official residence of the governor of New Jersey, known as Drumthwacket, is located in Princeton, and is listed on both the U.S. National Register of Historic Places and the New 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 fictional Martian 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 his The War of the Worlds invasion. His imaginary aliens first "landed" at what is now West Windsor. A commemorative monument is erected at Grovers Mill park."War of the Worlds Monument" , South Suburban College. Accessed October 17, 2008.
There were 27 Mercer County residents killed during the September 11 terrorist attacks in Lower Manhattan. A long steel beam weighing one ton was given to the county by the Port Authority of New York and New Jersey in March 2011 and is now displayed at Mercer County Park.Staff. "Hughes, Officials unveil section of steel beam from Sept. 11 to be used in memorial" , 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."
Geography and climate According to the U.S. Census Bureau, as of the 2020 Census, the county had a total area of , of which was land (98.1%) and was water (1.9%).2020 Census Gazetteer File for Counties in New Jersey, United States Census Bureau. Accessed April 1, 2023.
The county is generally flat and low-lying on the inner coastal plain, which extends up to the Route 1 corridor. Further northwest, terrain rises as it ascends the Piedmont Plateau, with The Sourlands encompassing the far northwestern portion of the county. Baldpate Mountain, in the western part of Hopewell Township, is the highest point in the county, at above sea level.New Jersey County High Points , Peakbagger.com. Accessed October 5, 2013. The lowest elevation is sea level, spread out along the shores of the tidal portions of the Delaware River, Crosswicks Creek and the smaller waterways within the Trenton-Hamilton Marsh in Hamilton Township and the city of Trenton.
Climate Most of Mercer has a hot-summer humid continental climate (Dfa) except for the southern portion of the county near and including Trenton where a humid subtropical climate (Cfa) exists. The hardiness zones are 6b and 7a.
Ecology According to the A. W. Kuchler U.S. potential natural vegetation types, most of Mercer County would have a dominant vegetation type of Appalachian Oak (104) with a dominant vegetation form of Eastern Hardwood Forest (25) with a dominant section of Northeastern Oak/Pine (110) Southern Mixed Forest (26) in the far east near Hightstown.U.S. Potential Natural Vegetation, Original Kuchler Types, v2.0 (Spatially Adjusted to Correct Geometric Distortions), Data Basin, Accessed June 24, 2023.
Demographics
2020 census