Bergen County is the most populous county in the U.S. state of New Jersey. Located in the northeastern corner of New Jersey, Bergen County and its many inner suburbs constitute a highly developed part of the New York City metropolitan area, bordering the Hudson River; the George Washington Bridge, which crosses the Hudson, connects Bergen County with Manhattan. The county is part of the North Jersey region of the state.

As of the 2020 United States census, the county's population was 955,732, its highest decennial count ever and an increase of 50,616 (+5.6%) from the 905,116 recorded at the 2010 census, which in turn reflected an increase of 20,998 (2.4%) from the 884,118 counted in the 2000 census. The United States Census Bureau's Population Estimates Program estimated a 2024 population of 978,641, an increase of 22,909 (+2.4%) from the 2020 decennial census.

The county is divided into 70 municipalities, the most of any county in New Jersey, made up of 56 boroughs, nine townships, three cities, and two villages. Its most populous place, with 46,030 residents as of the 2020 census, is Hackensack, which is also its county seat. Mahwah covers the largest area of any municipality, at 26.19 square miles (67.8 km²).

Bergen County is one of the largest commercial hubs in both New Jersey and the United States, generating over $6 billion in annual revenues from retailers in Paramus alone, despite blue laws keeping most stores in the county and especially Paramus itself (which has even stricter blue laws than the rest of the county) open only six days per week. The county is one of the wealthiest counties in the United States, with a median household income of $109,497 (compared to $89,703 in New Jersey and $69,021 nationwide) and a per capita income of $55,710 (vs. $46,691 in the state and $37,638 in the U.S.) as of the 2017–2021 American Community Survey. Bergen County has some of the highest home prices in the United States, with the median sale price approximately $900,000 as of 2025 and maximum prices in the tens of millions of dollars. The county's park system covers more than 9,000 acres (3,600 ha).

The origin of the name of Bergen County is a matter of debate. It is believed that the county is named after one of the earliest settlements, Bergen, in modern-day Hudson County, New Jersey. Several sources also attribute the name to Bergen, Norway, while others attribute it to Bergen op Zoom in the Netherlands. Some sources say that the name is derived from one of the earliest settlers of New Amsterdam (now New York City), Hans Hansen Bergen, a native of Norway, who arrived in New Netherland in 1633.

At the time of first European contact, Bergen County was inhabited by Native American people, particularly the Lenape Nation, whose subgroups included the Tappan, Hackensack, and Rumachenanck (later called the Haverstraw), as named by the Dutch colonists. Some of their descendants are included among the Ramapough Mountain Indians, recognized as a tribe by the state in 1980. Their ancestors had moved into the mountains to escape encroachment by Dutch and English colonists. Their descendants reside mostly in the northwest of the county, in nearby Passaic County and in Rockland County, New York, tracing their Lenape ancestry to speakers of the Munsee language, one of three major dialects of their language. Over the years, they absorbed other ethnicities by intermarriage.

In the 17th century, the Dutch considered the area comprising today's Bergen and Hudson counties as part of New Netherland, their colonial province of the Dutch Republic. The Dutch claimed it after Henry Hudson (sailing for the Dutch East India Company) explored Newark Bay and anchored his ship at Weehawken Cove in 1609. From an early date, the Dutch began to import African slaves to fill their labor needs. Bergen County eventually was the largest slaveholding county in the state, with nearly 20% of its population consisting of slaves in 1800. The African slaves were used for labor at the ports to support shipping, as well as for domestic servants, trades, and farm labor.

Early settlement attempts by the Dutch colonists included Pavonia (1633), Vriessendael (1640), and Achter Col (1642), but the Native Americans repelled these settlements in Kieft's War (1643–1645) and the Peach War (1655). European settlers returned to the western shores of the Hudson River in the 1660 formation of Bergen Township (now part of Jersey City, New Jersey), which would become one of the earliest permanent European settlements in present-day New Jersey.