Carlstadt is a borough in Bergen County, in the U.S. state of New Jersey. As of the 2020 United States census, the borough's population was 6,372, an increase of 245 from the 2010 census count of 6,127, which in turn reflected an increase of 210 from the 5,917 counted in the 2000 census. Carlstadt was originally formed as a village by an act of the New Jersey Legislature on March 12, 1860, within Lodi Township.