Elmer is a borough in Salem County in the U.S. state of New Jersey. As of the 2010 United States Census, the borough's population was 1,395, reflecting an increase of 11 (+0.8%) from the 1,384 counted in the 2000 Census, which had in turn declined by 187 (-11.9%) from the 1,571 counted in the 1990 Census. It is the home of the annual Appel Farm Arts and Music Festival, which celebrated its 23rd year in 2012.