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 from the 1,384 counted in the 2000 Census, which had in turn declined by 187 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.