Keansburg is a borough in Monmouth County, in the U.S. state of New Jersey. As of the 2020 United States census, the borough's population was 9,755, a decrease of 350 (−3.5%) from the 2010 census count of 10,105, which in turn reflected a decline of 627 (−5.8%) from 10,732 in the 2000 census.

Monmouth County is a county, located in the central section of the U.S. state of New Jersey. Comprising much of the northern half of the Jersey Shore, 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. Monmouth County's geographic area comprises 30% water. The county is considered part of the Central Jersey region of the state, though it was not among the four counties explicitly listed as included in Central Jersey as part of legislation signed into law in 2023.