Caldwell is a borough located in northwestern Essex County, in the U.S. state of New Jersey, about 16 miles (26 km) west of New York City and 6 miles (9.7 km) north-west of Newark, the state's most populous city. As of the 2020 United States census, the borough's population was 9,027, an increase of 1,205 (+15.4%) from the 2010 census count of 7,822, which in turn reflected an increase of 238 (+3.1%) from the 7,584 counted in the 2000 census.
Caldwell was incorporated as a borough by an act of the New Jersey Legislature on February 10, 1892, from portions of Caldwell Township (now Fairfield Township), based on the results of a referendum held on the previous day. In 1981, the borough's name was changed to the "Township of the Borough of Caldwell", as one of seven Essex County municipalities to pass a referendum to become a township, joining four municipalities that had already made the change, of what would ultimately be more than a dozen Essex County municipalities to reclassify themselves as townships in order take advantage of federal revenue sharing policies that allocated townships a greater share of government aid to municipalities on a per capita basis. Effective January 26, 1995, it again became a borough.