Monmouth County is a county located in Central New Jersey, in the United States within the New York metropolitan area and located in the central part of the state. It is the northernmost county along the Jersey Shore. As of the 2010 Census, the population was 630,380, up from 615,301 at the 2000 Census, falling 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 , 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.
On October 29, 2012, Hurricane Sandy caused catastrophic damage to coastal areas of Monmouth County. As Sandy's surge arrived in Monmouth County, flood levels of above normal were measured at Sandy Hook shortly before the destruction of the tidal station, breaking all previous local records. The surge caused waves as high as , measured where the Sandy Hook Bay meets the New York Bay.
An English navigator, Henry Hudson, and his crew aboard the Dutch vessel Half Moon, in 1609, spotted land in what is now Monmouth County, most likely off Sandy Hook; however, some historical accounts credit this landing to present-day Keansburg. Among the first European settlers in the area were a group of Quaker families from Long Island who settled the Monmouth Tract, an early land grant from Richard Nicolls issued in 1665. They were followed by a group of Scottish settlers who inhabited Freehold Township in about 1682-85, followed several years later by Dutch settlers. As they arrived in this area, they were greeted by Lenape Native Americans, who lived in scattered small family bands and developed a largely amicable relationship with the new arrivals. Enslaved Africans were present in the area from at least 1680, and by 1726 made up 9% of the total population of the county.
Its name may come from the Rhode Island Monmouth Society or from a suggestion from Colonel Lewis Morris that the county should be named after Monmouthshire in Wales, Great Britain. Other suggestions include that it was named for James Scott, 1st Duke of Monmouth (1649–1685), who had many allies among the East Jersey leadership. In 1714, the first county government was established.
At the June 28, 1778, Battle of Monmouth, near Freehold Township, General George Washington's soldiers battled the British under Sir Henry Clinton, in the longest land battle of the American Revolutionary War. It was at Monmouth that the tactics and training from Friedrich Wilhelm von Steuben developed at Valley Forge during the winter encampment were first implemented on a large scale.
At independence, Monmouth's population included 1,640 slaves, as well as an undetermined number of free African Americans. The number of enslaved persons fell steeply after 1820, though a small number remained until at least 1850. Monmouth's free African American population climbed from 353 in 1790 to 2,658 in 1860.