Key facts
- Country
- United States
- State
- New Jersey
- Named after
- Monmouthshire , Wales
- Seat
- Freehold Borough
- Largest city
- Middletown Township (population), Howell Township (area)
- Commissioner director
- Thomas A. Arnone ( R , term ends December 31, 2025)
- Total
- 661.40 sq mi (1,713.0 km )
- Land
- 468.18 sq mi (1,212.6 km )
- Water
- 193.22 sq mi (500.4 km ) 29.2%
- Estimate 2025
- 651,035
- Density
- 1,374.7/sq mi (530.78/km )
- Time zone
- UTC−5 ( Eastern )
Article
Monmouth County (/ˈmɒnməθ/) is a county located in the central portion of the U.S. state of New Jersey. It is bordered to its west by Mercer and Middlesex Counties, to its south by Ocean County, to its east by the Atlantic Ocean, and to its north by the Raritan Bay (sharing a border with the boroughs of Staten Island, Brooklyn, and Queens in New York City, across it). Monmouth County's geographic area comprises 30% water. The county is part of the Jersey Shore region of the state.
As of the 2020 United States census, the county was the state's fifth-most-populous county with a population of 643,615, its highest decennial count ever and an increase of 13,235 (+2.1%) from the 2010 census count of 630,380, which in turn reflected an increase of 15,079 from 615,301 at the 2000 census. As of 2010, the county fell to the fifth-most populous county in the state, having been surpassed by Hudson County. The United States Census Bureau's Population Estimates Program estimated a 2025 population of 651,035, an increase of 7,420 (+1.2%) from the 2020 decennial census.