Carlstadt is a borough in Bergen County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 6,127, reflecting an increase of 210 (+3.5%) from the 5,917 counted in the 2000 Census, which had in turn increased by 407 (+7.4%) from the 5,510 counted in the 1990 Census.
Carlstadt was originally formed as a village by an Act of the New Jersey Legislature on March 12, 1860, within Lodi Township. It was named after Dr. Carl Klein, the leader of a group of early German settlers who led the project to establish the community. The Borough of Carlstadt was incorporated on June 27, 1894, formally set off from Bergen Township, at the height of the Boroughitis phenomenon then sweeping through Bergen County.