Lambertville is a city within Hunterdon County in the U.S. state of New Jersey. As of the 2020 United States census, the city's population was 4,139, an increase of 233 from the 3,906 recorded at the 2010 census, which in turn had reflected an increase of 38 from the 3,868 counted at the 2000 census. Lambertville is situated on the banks of the Delaware River in southwestern Hunterdon County, directly across the river from New Hope, Pennsylvania.