Ocean County is a county in the U.S. state of New Jersey, and the southernmost county in the New York metropolitan area. The county borders the Atlantic Ocean on the east and in terms of total area is the state's largest county. Its county seat is Toms River. The county is part of the Jersey Shore region of the state.

Since 2020, Ocean County has been the fastest-growing county in New Jersey, with a population of 637,229 recorded at the 2020 United States census, its highest decennial count ever and ranking the county as the state's sixth-most populous county, with an increase of 60,662 (+10.5%) from the 576,567 enumerated at the 2010 census, which in turn reflected an increase of 65,651 (+12.8%) from the 510,916 counted in the 2000 census. Since 2010, Ocean County's population has been growing faster than the United States as a whole. The United States Census Bureau's Population Estimates Program estimated a 2025 population of 673,746, an increase of 36,517 (+5.7%) from the 2020 decennial census. Ocean County’s most populous and fastest-growing place is Lakewood Township, with an estimated 139,866 residents as of 2023, while Jackson Township covers 100.62 square miles (260.6 km²), the largest total area of any municipality in the county.

Ocean County is located 50 miles (80 km) east of Philadelphia, 70 miles (110 km) south of New York City, and 25 miles (40 km) north of Atlantic City, making it a prime vacation destination for residents of these cities during the summer. As with the entire Jersey Shore, summer traffic routinely clogs local roadways throughout the season. Over 31% of Ocean County's total area is water.

Ocean County is part of the New York metropolitan area. The county is also home to many tourist attractions frequented by Philadelphia metropolitan area residents, including the beachfront communities of Seaside Heights, Long Beach Island, and Point Pleasant Beach, and Six Flags Great Adventure, an amusement park in Jackson Township that was the home to the world's tallest and second-fastest roller coaster, Kingda Ka. Ocean County is a gateway to New Jersey's Pine Barrens, one of the largest protected land areas on the East Coast.

Paleo-Indians migrated to what is now Ocean County around 11,500 BC.

Prior to its creation, Ocean County was almost entirely within Shrewsbury Township in Monmouth County, with the exception of Tuckerton and Little Egg Harbor Township. Ocean County was established on February 15, 1850, from portions of Monmouth county; Little Egg Harbor Township was annexed from Burlington County on March 30, 1891. It derives its name from the Atlantic Ocean that it borders.

In 1964, Ocean County College opened.

The most populous municipality in the county is the rapidly growing Lakewood Township with 135,158 residents in 2020, its highest decennial count ever and an increase of 42,315 (+45.6%) from its 2010 census count of 92,843. Jackson Township, which covers 100.62 square miles (260.6 km²), is the largest municipality in Ocean County by area.