Penns Grove is a borough in Salem County, in the U.S. state of New Jersey. As of the 2020 United States census, the borough's population was 4,837, a decrease of 310 from the 2010 census count of 5,147, which in turn reflected an increase of 261 from the 4,886 counted in the 2000 census. Penns Grove had the fourth-highest property tax rate in New Jersey, with an equalized rate of 5.556% in 2020, compared to 3.476% in Salem County and a statewide average of 2.279%.