Bergen County is the most populous county of the state of New Jersey, United States. As of the 2000 Census, the population is 884,118. It is part of the New York Metropolitan Area. Its county seat is Hackensack. Bergen County ranks as the 21st among the highest-income counties in the United States with a per capita income of $33,638.

According to the U.S. Census Bureau, the county has a total area of 639 km² (247 mi²). 606 km² (234 mi²) of it is land and 33 km² (13 mi²) of it (5.12%) is water.

The highest elevation is Bald Mountain near the New York state line in Mahwah, at 1,164 feet (355 m) above sea level. The lowest point is sea level, along the Hudson River.

The sharp cliffs of the New Jersey Palisades lift much the county up from the river along the eastern boundary with the Hudson River, but then relief remains relatively minimal across the county as much of it is in the Hackensack River valley. Only in the northwestern portion of the county are any serious hills found, leading to the Ramapo Mountains. The damming of the Hackensack River (and tributaries) produced three reservoirs in the county, Woodcliff Lake Reservoir, Lake Tappan and Oradell Reservoir, which provide drinking water to much of northern New Jersey. The Hackensack River drains through the New Jersey Meadowlands, a wetlands area in the southern portion of the county.

Bergen County is bordered by Rockland County, New York to the north, by Westchester County, the Bronx, and Manhattan in New York, across the Hudson River to the east, Hudson County to the south, a small border with Essex County also to the south and Passaic County to the west.