Monmouth County is a county located in Central New Jersey, in the United States within the New York metropolitan area, and the northernmost county along the Jersey Shore. As of the 2017 Census estimate, the county’s population was 626,351, making it the state’s fifth-most populous county, representing a decrease of 0.6% from the 2010 Census, when the population was enumerated at 630,380, in turn 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. Its county seat is Freehold Borough. The most populous place was Middletown Township, with 66,522 residents at the time of the 2010 Census, while Howell Township covered 61.21 square miles (158.5 km2), the largest total area of any municipality.
Monmouth County ranked 38th among the highest-income counties in the United States as of 2011, placing it among the top 1.2% of counties by wealth. As of 2009, it was ranked 56th in the United States by personal per-capita income.
As of October 31, 2014, there were a total of 428,452 registered voters in Monmouth County, of whom 101,850 (23.8%) were registered as Democrats, 98,404 (23.%) were registered as Republicans and 227,823 (53.2%) were registered as Unaffiliated. There were 375 voters registered to other parties. Among the county’s 2010 Census population, 89% of residents of age 18 and over were registered to vote.